Set up default currency accounts automatically (#72)

backend/product/app/runtime/services.go

@@ -75,6 +75,7 @@ func OpenDependencies(_ context.Context, logger mlogger.Logger, config *api.Conf
 				return nil, nil, err
 			}
 			deps.Payments = &payments.Service{Store: paymentStore, Provider: provider, Identity: deps.Identity, Logger: logger.Named("payments")}
+			deps.Auth.Wallet = deps.Payments
 			logger.Info("Sendico sign-up facts integration enabled")
 		}
 		records, err := factorstore.Open(logger, db)

backend/product/auth/flow/service.go

@@ -31,8 +31,13 @@ type SignupFacts interface {
 	Ready(context.Context, bson.ObjectID) error
 }
 
+type CurrencyAccounts interface {
+	Ensure(context.Context, *customer.Account) error
+}
+
 type Service struct {
 	Facts         SignupFacts
+	Wallet        CurrencyAccounts
 	Accounts      account.DB
 	Customers     accountservice.AccountService
 	Tokens        verification.DB
@@ -110,6 +115,11 @@ func (s *Service) Signup(ctx context.Context, a *customer.Account, ip, key strin
 			return nil, err
 		}
 	}
+	if s.Wallet != nil {
+		if err := s.Wallet.Ensure(ctx, a); err != nil {
+			return nil, err
+		}
+	}
 	if raw != "" {
 		u, _ := url.Parse(s.ActivationURL)
 		q := u.Query()
@@ -148,6 +158,11 @@ func (s *Service) ResendActivation(ctx context.Context, email, ip, key string) e
 			return err
 		}
 	}
+	if s.Wallet != nil {
+		if err := s.Wallet.Ensure(ctx, a); err != nil {
+			return err
+		}
+	}
 	_, err = s.sendActivation(ctx, a, key)
 	return err
 }

backend/product/auth/http/v1/public/verification_integration_test.go

@@ -75,6 +75,17 @@ func (m *capturedMail) Send(_ context.Context, r notifications.Message) error {
 	}
 	return nil
 }
+
+type signupWallet struct {
+	customers []bson.ObjectID
+	err       error
+}
+
+func (s *signupWallet) Ensure(_ context.Context, a *customer.Account) error {
+	s.customers = append(s.customers, a.ID)
+	return s.err
+}
+
 func TestSignupActivationAndLoginEmailFlow(t *testing.T) {
 	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
 	defer cancel()
@@ -102,6 +113,8 @@ func TestSignupActivationAndLoginEmailFlow(t *testing.T) {
 	require.NoError(t, err)
 	provider := &signupProvider{fail: true}
 	service.Facts = &identity.Service{Store: bindings, Provider: provider, Logger: zap.NewNop()}
+	wallet := &signupWallet{err: merrors.ServiceUnavailable("account setup temporarily unavailable")}
+	service.Wallet = wallet
 	// Keep the real verification/customer stores and capture only session writes.
 	sessions := &testRefreshTokenDB{client: &session.Client{ClientID: "web"}}
 	records, err := factorstore.Open(zap.NewNop(), factory)
@@ -133,6 +146,14 @@ func TestSignupActivationAndLoginEmailFlow(t *testing.T) {
 	signup["name"] = "Changed retry name"
 	provider.fail = false
 	w = post("signup", signup)
+	require.Equal(t, 503, w.Code, w.Body.String())
+	require.Empty(t, mail.messages)
+	require.Len(t, wallet.customers, 1)
+	w = post("verification/send", map[string]string{"email": "user@example.com", "idempotencyKey": "wallet-retry"})
+	require.Equal(t, 503, w.Code, w.Body.String())
+	require.Empty(t, mail.messages)
+	wallet.err = nil
+	w = post("signup", signup)
 	require.Equal(t, 202, w.Code, w.Body.String())
 	require.Equal(t, 1, provider.registrations)
 	require.Equal(t, "Customer", provider.last.FullName)
@@ -149,6 +170,7 @@ func TestSignupActivationAndLoginEmailFlow(t *testing.T) {
 	require.NoError(t, err)
 	require.False(t, a.IsActive())
 	require.Equal(t, a.ID.Hex(), provider.last.CustomerRef)
+	require.Equal(t, []bson.ObjectID{a.ID, a.ID, a.ID}, wallet.customers)
 	require.NoError(t, service.Facts.Ready(ctx, a.ID))
 	login := map[string]any{"login": map[string]string{"login": "user@example.com", "password": " correct password "}, "clientId": "web", "deviceId": "browser"}
 	require.Equal(t, 403, post("login", login).Code)

backend/product/payments/accounts.go

@@ -0,0 +1,50 @@
+package payments
+
+import (
+	"context"
+	"time"
+
+	customer "git.sendico.io/tech/sxchnge/product/customers/model"
+	merrors "git.sendico.io/tech/sxchnge/shared/errors"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	"go.uber.org/zap"
+)
+
+var accountSetup = promauto.NewCounterVec(prometheus.CounterOpts{Name: "sxchnge_currency_accounts_setup_total", Help: "Default currency account setup attempts, including checks of existing accounts."}, []string{"outcome"})
+var accountSetupDuration = promauto.NewHistogram(prometheus.HistogramOpts{Name: "sxchnge_currency_accounts_setup_duration_seconds", Help: "Time to confirm all default currency accounts exist."})
+
+func (s *Service) Ensure(ctx context.Context, a *customer.Account) error {
+	_, err := s.ensureAccounts(ctx, a)
+	if err != nil {
+		return merrors.ServiceUnavailableWrap(err, "currency account setup unavailable")
+	}
+	return nil
+}
+
+func (s *Service) ensureAccounts(ctx context.Context, a *customer.Account) (subject string, result error) {
+	started := time.Now()
+	defer func() {
+		outcome := "ready"
+		if result != nil {
+			outcome = "failed"
+		}
+		accountSetup.WithLabelValues(outcome).Inc()
+		accountSetupDuration.Observe(time.Since(started).Seconds())
+	}()
+	if s == nil || s.Identity == nil || s.Provider == nil {
+		return "", Unavailable
+	}
+	if a == nil || a.ID.IsZero() {
+		return "", NotFound
+	}
+	subject, result = s.Identity.Subject(ctx, a)
+	if result != nil {
+		return "", result
+	}
+	if result = s.Provider.EnsureAccounts(ctx, subject); result != nil {
+		s.Logger.Warn("Currency account setup incomplete", zap.String("account_ref", a.ID.Hex()), zap.Error(result))
+		return "", result
+	}
+	return subject, nil
+}

backend/product/payments/accounts_test.go

@@ -0,0 +1,28 @@
+package payments
+
+import (
+	"testing"
+
+	customer "git.sendico.io/tech/sxchnge/product/customers/model"
+	"github.com/stretchr/testify/require"
+	"go.mongodb.org/mongo-driver/v2/bson"
+	"go.uber.org/zap"
+)
+
+func TestSignupAndWalletReadEnsureCustomerCurrencyAccounts(t *testing.T) {
+	a := &customer.Account{}
+	a.ID = bson.NewObjectID()
+	p := &provider{namespace: "provider"}
+	s := &Service{Provider: p, Identity: identity{}, Logger: zap.NewNop(), Factors: &factors{}, Store: &memoryStore{records: map[bson.ObjectID]Record{}}}
+	require.NoError(t, s.Ensure(t.Context(), a))
+	require.Equal(t, "subject", p.setupSubject)
+	snapshot, err := s.Fetch(t.Context(), a)
+	require.NoError(t, err)
+	require.Len(t, snapshot.Accounts, 1)
+	require.Equal(t, 2, p.setupCalls)
+	p.setupErr = Unavailable
+	_, err = s.Fetch(t.Context(), a)
+	require.ErrorIs(t, err, Unavailable)
+	require.Error(t, s.Ensure(t.Context(), a))
+	require.Error(t, s.Ensure(t.Context(), nil))
+}

backend/product/payments/model.go

@@ -53,6 +53,7 @@ func (*Record) Collection() string { return "payment_quotes" }
 
 type Provider interface {
 	Namespace() string
+	EnsureAccounts(context.Context, string) error
 	Accounts(context.Context, string) ([]Account, error)
 	Quote(context.Context, string, Request, []Account) (Quote, error)
 	Execute(context.Context, string, string) (RemoteOperation, error)

backend/product/payments/service.go

@@ -206,7 +206,7 @@ func (s *Service) Fetch(ctx context.Context, a *customer.Account) (Snapshot, err
 	if err := s.ready(); err != nil {
 		return Snapshot{}, err
 	}
-	subject, err := s.Identity.Subject(ctx, a)
+	subject, err := s.ensureAccounts(ctx, a)
 	if err != nil {
 		return Snapshot{}, err
 	}

backend/product/payments/service_test.go

@@ -76,15 +76,25 @@ func (s *memoryStore) Attach(_ context.Context, r *Record, id string) error {
 }
 
 type provider struct {
-	mu        sync.Mutex
-	accepted  int
-	lost      bool
-	status    string
-	key       string
-	namespace string
+	mu           sync.Mutex
+	accepted     int
+	lost         bool
+	status       string
+	key          string
+	namespace    string
+	setupCalls   int
+	setupSubject string
+	setupErr     error
 }
 
 func (p *provider) Namespace() string { return p.namespace }
+func (p *provider) EnsureAccounts(_ context.Context, subject string) error {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	p.setupCalls++
+	p.setupSubject = subject
+	return p.setupErr
+}
 func (p *provider) Accounts(context.Context, string) ([]Account, error) {
 	return []Account{{ID: "ledger", Currency: "EUR", Precision: 2, Available: 5000}}, nil
 }

backend/product/providers/sendico/accounts.go

@@ -0,0 +1,87 @@
+package sendico
+
+import (
+	"context"
+	"net/http"
+
+	"git.sendico.io/tech/sxchnge/product/payments"
+	merrors "git.sendico.io/tech/sxchnge/shared/errors"
+)
+
+func (c *Client) validCustomerAccount(a accountDTO, subject string) bool {
+	return validRef(a.ID) && a.ScopeRef == c.config.OrganizationID && a.Owner == "" &&
+		a.Type == "ACCOUNT_TYPE_ASSET" && a.LedgerRole == "ACCOUNT_ROLE_OPERATING" &&
+		a.Status == "ACCOUNT_STATUS_ACTIVE" && !a.AllowNegative && a.Metadata["sxchnge_subject_ref"] == subject &&
+		(a.Metadata["external_subject_ref"] == "" || a.Metadata["external_subject_ref"] == subject)
+}
+
+// EnsureAccounts also repairs older customers, using provider-enforced
+// organization/subject/currency uniqueness for safe retries after lost responses.
+func (c *Client) EnsureAccounts(ctx context.Context, subject string) error {
+	if !validRef(subject) {
+		return payments.Unavailable
+	}
+	root := "/ledger_accounts/" + c.config.OrganizationID
+	var data accountListDTO
+	if err := c.paymentRequest(ctx, http.MethodGet, root, nil, &data); err != nil {
+		return err
+	}
+	existing := map[string]bool{}
+	reconcile := map[string]bool{}
+	for _, a := range data.Accounts {
+		if a.Metadata["sxchnge_subject_ref"] != subject && a.Metadata["external_subject_ref"] != subject {
+			continue
+		}
+		if !c.validCustomerAccount(a, subject) || existing[a.Currency] {
+			return payments.Unavailable
+		}
+		existing[a.Currency] = true
+		reconcile[a.Currency] = a.Metadata["external_subject_ref"] == subject
+	}
+	missing := []string{}
+	for _, code := range []string{"RUB", "USDT", "USDC"} {
+		if !existing[code] || reconcile[code] {
+			missing = append(missing, code)
+		}
+	}
+	if len(missing) == 0 {
+		return nil
+	}
+	// Older providers can accept the metadata but cannot prevent duplicates.
+	// Require the explicit capability before issuing the first create.
+	if !data.ExternalSubjectAccounts {
+		return payments.Unavailable
+	}
+	var catalog struct {
+		Rows []currencyDTO `json:"currencies"`
+	}
+	if err := c.paymentRequest(ctx, http.MethodGet, "/payments/fx/currencies/"+c.config.OrganizationID, nil, &catalog); err != nil {
+		return err
+	}
+	for _, code := range missing {
+		found := false
+		for _, currency := range catalog.Rows {
+			if currency.Code == code && currency.Scale != nil && *currency.Scale >= 0 && *currency.Scale <= 8 {
+				found = true
+			}
+		}
+		if !found {
+			return merrors.OpaqueWrap(payments.Unavailable, payments.Unsupported, "default currency missing from provider catalog")
+		}
+	}
+	// Replaying a bound create also resumes Sendico's durable wallet/route setup
+	// if a previous response failed after the ledger itself had been committed.
+	for _, code := range missing {
+		var response struct {
+			Account accountDTO `json:"account"`
+		}
+		request := createAccountDTO{Currency: code, Type: "asset", LedgerRole: "operating", Metadata: map[string]string{"external_subject_ref": subject, "sxchnge_subject_ref": subject}}
+		if err := c.paymentRequest(ctx, http.MethodPost, root, request, &response, http.StatusCreated); err != nil {
+			return err
+		}
+		if !c.validCustomerAccount(response.Account, subject) || response.Account.Currency != code || response.Account.Metadata["external_subject_ref"] != subject {
+			return payments.Unavailable
+		}
+	}
+	return nil
+}

backend/product/providers/sendico/accounts_test.go

@@ -0,0 +1,200 @@
+package sendico
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"go.mongodb.org/mongo-driver/v2/bson"
+)
+
+type accountServer struct {
+	mu              sync.Mutex
+	rows            []accountDTO
+	posts           []string
+	capable         bool
+	missingCurrency bool
+	failCurrency    string
+	loseResponse    bool
+	wrongResponse   bool
+}
+
+func customerLedger(code string) accountDTO {
+	return accountDTO{ID: bson.NewObjectID().Hex(), ScopeRef: org, Currency: code, Type: "ACCOUNT_TYPE_ASSET", LedgerRole: "ACCOUNT_ROLE_OPERATING", Status: "ACCOUNT_STATUS_ACTIVE", Metadata: map[string]string{"sxchnge_subject_ref": subject, "external_subject_ref": subject}}
+}
+
+func (s *accountServer) serve(t *testing.T) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		s.mu.Lock()
+		defer s.mu.Unlock()
+		require.NotEmpty(t, r.Header.Get("Authorization"))
+		var data any
+		switch {
+		case strings.Contains(r.URL.Path, "/currencies/"):
+			rows := []map[string]any{{"code": "RUB", "accountingScale": 2}, {"code": "USDT", "accountingScale": 6}, {"code": "USDC", "accountingScale": 6}}
+			if s.missingCurrency {
+				rows = rows[:2]
+			}
+			data = map[string]any{"currencies": rows}
+		case r.Method == http.MethodPost:
+			var request createAccountDTO
+			require.NoError(t, json.NewDecoder(r.Body).Decode(&request))
+			require.Equal(t, "asset", request.Type)
+			require.Equal(t, "operating", request.LedgerRole)
+			require.False(t, request.AllowNegative)
+			require.Equal(t, subject, request.Metadata["external_subject_ref"])
+			require.Equal(t, subject, request.Metadata["sxchnge_subject_ref"])
+			s.posts = append(s.posts, request.Currency)
+			if s.failCurrency == request.Currency {
+				s.failCurrency = ""
+				w.WriteHeader(503)
+				return
+			}
+			var row accountDTO
+			for _, a := range s.rows {
+				if a.Currency == request.Currency && a.Metadata["external_subject_ref"] == subject {
+					row = a
+				}
+			}
+			if row.ID == "" {
+				row = customerLedger(request.Currency)
+				s.rows = append(s.rows, row)
+			}
+			if s.loseResponse {
+				s.loseResponse = false
+				w.WriteHeader(503)
+				return
+			}
+			if s.wrongResponse {
+				row.Currency = "EUR"
+			}
+			w.WriteHeader(http.StatusCreated)
+			data = map[string]any{"account": row}
+		case strings.HasSuffix(r.URL.Path, "/balance"):
+			parts := strings.Split(r.URL.Path, "/")
+			data = map[string]any{"balance": balanceDTO{ID: parts[len(parts)-2], Money: moneyDTO{Amount: "45.00", Currency: "RUB"}}}
+		default:
+			data = map[string]any{"accounts": s.rows, "externalSubjectAccounts": s.capable}
+		}
+		require.NoError(t, json.NewEncoder(w).Encode(map[string]any{"status": "success", "data": data}))
+	}
+}
+
+func TestEnsureCurrencyAccountsPreservesExistingAndRecoversPartialFailure(t *testing.T) {
+	for _, lost := range []bool{false, true} {
+		t.Run(map[bool]string{false: "partial failure", true: "lost response"}[lost], func(t *testing.T) {
+			s := &accountServer{capable: true, failCurrency: "USDT", loseResponse: lost}
+			if lost {
+				s.failCurrency = ""
+			}
+			server := httptest.NewServer(s.serve(t))
+			defer server.Close()
+			c, err := Open(config(t, server.URL))
+			require.NoError(t, err)
+			require.Error(t, c.EnsureAccounts(t.Context(), subject))
+			require.Len(t, s.rows, 1)
+			firstID := s.rows[0].ID
+			require.NoError(t, c.EnsureAccounts(t.Context(), subject))
+			require.NoError(t, c.EnsureAccounts(t.Context(), subject))
+			require.Len(t, s.rows, 3)
+			require.Equal(t, firstID, s.rows[0].ID)
+			// Bound creates are replayed to finish interrupted wallet/route setup;
+			// the provider must return the original ledger each time.
+			require.Equal(t, 3, countCurrency(s.posts, "RUB"))
+		})
+	}
+}
+
+func countCurrency(rows []string, code string) int {
+	n := 0
+	for _, r := range rows {
+		if r == code {
+			n++
+		}
+	}
+	return n
+}
+
+func TestEnsureAccountsConcurrentRequestsUseStableSubjectBinding(t *testing.T) {
+	s := &accountServer{capable: true}
+	server := httptest.NewServer(s.serve(t))
+	defer server.Close()
+	c, err := Open(config(t, server.URL))
+	require.NoError(t, err)
+	errors := make(chan error, 12)
+	for range 12 {
+		go func() { errors <- c.EnsureAccounts(t.Context(), subject) }()
+	}
+	for range 12 {
+		require.NoError(t, <-errors)
+	}
+	require.Len(t, s.rows, 3)
+}
+
+func TestEnsureAccountsRejectsUnsafeProviderStateBeforeCreating(t *testing.T) {
+	for _, kind := range []string{"old provider", "missing currency", "frozen", "owned", "negative", "duplicate", "wrong subject"} {
+		t.Run(kind, func(t *testing.T) {
+			s := &accountServer{capable: true}
+			a := customerLedger("RUB")
+			switch kind {
+			case "old provider":
+				s.capable = false
+			case "missing currency":
+				s.missingCurrency = true
+			case "frozen":
+				a.Status = "ACCOUNT_STATUS_FROZEN"
+				s.rows = []accountDTO{a}
+			case "owned":
+				a.Owner = source
+				s.rows = []accountDTO{a}
+			case "negative":
+				a.AllowNegative = true
+				s.rows = []accountDTO{a}
+			case "duplicate":
+				s.rows = []accountDTO{a, customerLedger("RUB")}
+			case "wrong subject":
+				a.Metadata["sxchnge_subject_ref"] = source
+				s.rows = []accountDTO{a}
+			}
+			server := httptest.NewServer(s.serve(t))
+			defer server.Close()
+			c, err := Open(config(t, server.URL))
+			require.NoError(t, err)
+			require.Error(t, c.EnsureAccounts(t.Context(), subject))
+			require.Empty(t, s.posts)
+		})
+	}
+}
+
+func TestEnsureAccountsValidatesCreateReceipt(t *testing.T) {
+	s := &accountServer{capable: true, wrongResponse: true}
+	server := httptest.NewServer(s.serve(t))
+	defer server.Close()
+	c, err := Open(config(t, server.URL))
+	require.NoError(t, err)
+	require.Error(t, c.EnsureAccounts(t.Context(), subject))
+	require.Len(t, s.posts, 1)
+}
+
+func TestEnsureAccountsKeepsExistingBindingsAndBalances(t *testing.T) {
+	a := customerLedger("RUB")
+	delete(a.Metadata, "external_subject_ref")
+	s := &accountServer{capable: true, rows: []accountDTO{a}}
+	server := httptest.NewServer(s.serve(t))
+	defer server.Close()
+	c, err := Open(config(t, server.URL))
+	require.NoError(t, err)
+	require.NoError(t, c.EnsureAccounts(t.Context(), subject))
+	require.Equal(t, []string{"USDT", "USDC"}, s.posts)
+	// A subsequent read uses the original RUB ledger and its authoritative funds.
+	s.rows = s.rows[:1]
+	accounts, err := c.Accounts(t.Context(), subject)
+	require.NoError(t, err)
+	require.Len(t, accounts, 1)
+	require.Equal(t, a.ID, accounts[0].ID)
+	require.EqualValues(t, 4500, accounts[0].Available)
+}

backend/product/providers/sendico/accounts_transport.go

@@ -0,0 +1,14 @@
+package sendico
+
+type accountListDTO struct {
+	Accounts                []accountDTO `json:"accounts"`
+	ExternalSubjectAccounts bool         `json:"externalSubjectAccounts"`
+}
+
+type createAccountDTO struct {
+	Currency      string            `json:"currency"`
+	Type          string            `json:"accountType"`
+	LedgerRole    string            `json:"role"`
+	AllowNegative bool              `json:"allowNegative"`
+	Metadata      map[string]string `json:"metadata"`
+}

backend/product/providers/sendico/payments.go

@@ -27,9 +27,7 @@ func (c *Client) Accounts(ctx context.Context, subject string) ([]payments.Accou
 			scales[row.Code] = *row.Scale
 		}
 	}
-	var data struct {
-		Accounts []accountDTO `json:"accounts"`
-	}
+	var data accountListDTO
 	root := "/ledger_accounts/" + c.config.OrganizationID
 	if err := c.paymentRequest(ctx, http.MethodGet, root, nil, &data); err != nil {
 		return nil, err
@@ -39,7 +37,7 @@ func (c *Client) Accounts(ctx context.Context, subject string) ([]payments.Accou
 		if row.Metadata["sxchnge_subject_ref"] != subject {
 			continue
 		}
-		if !validRef(row.ID) || row.ScopeRef != c.config.OrganizationID || row.Owner != "" || row.Status != "ACCOUNT_STATUS_ACTIVE" || row.Type != "ACCOUNT_TYPE_ASSET" || row.LedgerRole != "ACCOUNT_ROLE_OPERATING" {
+		if !c.validCustomerAccount(row, subject) {
 			return nil, payments.Unavailable
 		}
 		scale, ok := scales[row.Currency]

backend/product/providers/sendico/payments_transport.go

@@ -54,14 +54,15 @@ type paymentDTO struct {
 	Created time.Time       `json:"createdAt"`
 }
 type accountDTO struct {
-	ID         string            `json:"ledgerAccountRef"`
-	ScopeRef   string            `json:"organizationRef"`
-	Owner      string            `json:"ownerRef"`
-	Currency   string            `json:"currency"`
-	Type       string            `json:"accountType"`
-	LedgerRole string            `json:"role"`
-	Status     string            `json:"status"`
-	Metadata   map[string]string `json:"metadata"`
+	ID            string            `json:"ledgerAccountRef"`
+	ScopeRef      string            `json:"organizationRef"`
+	Owner         string            `json:"ownerRef"`
+	Currency      string            `json:"currency"`
+	Type          string            `json:"accountType"`
+	LedgerRole    string            `json:"role"`
+	Status        string            `json:"status"`
+	AllowNegative bool              `json:"allowNegative"`
+	Metadata      map[string]string `json:"metadata"`
 }
 type currencyDTO struct {
 	Code  string `json:"code"`
@@ -72,7 +73,7 @@ type balanceDTO struct {
 	Money moneyDTO `json:"balance"`
 }
 
-func (c *Client) paymentRequest(ctx context.Context, method, path string, payload, dst any) error {
+func (c *Client) paymentRequest(ctx context.Context, method, path string, payload, dst any, accepted ...int) error {
 	token, err := c.token()
 	if err != nil {
 		return err
@@ -98,7 +99,11 @@ func (c *Client) paymentRequest(ctx context.Context, method, path string, payloa
 	}
 	defer func() { _ = res.Body.Close() }()
 	// Never forward upstream errors, credentials, or arbitrary error bodies.
-	if res.StatusCode != http.StatusOK {
+	expected := http.StatusOK
+	if len(accepted) != 0 {
+		expected = accepted[0]
+	}
+	if res.StatusCode != expected {
 		return payments.Unavailable
 	}
 	var envelope struct {