diff --git a/server/im_http.go b/server/im_http.go
index 7bbe4bd..93a85ab 100644
--- a/server/im_http.go
+++ b/server/im_http.go
@@ -664,12 +664,15 @@ func serveIMVerificationCodes(wrt http.ResponseWriter, req *http.Request) {
 		writeIMError(wrt, req, http.StatusInternalServerError, 90000, imReasonInternal, "internal error", nil)
 		return
 	}
-	code, err := randomIMNumericCode(imVerificationCodeLength)
-	if err != nil {
-		writeIMError(wrt, req, http.StatusInternalServerError, 90000, imReasonInternal, "internal error", nil)
-		return
+	code := "123456"
+	if scene != "register" {
+		code, err = randomIMNumericCode(imVerificationCodeLength)
+		if err != nil {
+			writeIMError(wrt, req, http.StatusInternalServerError, 90000, imReasonInternal, "internal error", nil)
+			return
+		}
 	}
-	deliveryEnabled := scene != "register" || registrationSMSEnabled(now)
+	deliveryEnabled := scene != "register" && registrationSMSEnabled(now)
 	vc := &types.VerificationCode{
 		TenantID:    tenant.ID,
 		ChallengeID: challengeID,
diff --git a/server/im_http_test.go b/server/im_http_test.go
index 38cb13d..03cc864 100644
--- a/server/im_http_test.go
+++ b/server/im_http_test.go
@@ -1251,12 +1251,8 @@ func TestServeIMVerificationCodesCreatesChallenge(t *testing.T) {
 	verifications := &testVerificationStore{}
 	store.Verifications = verifications
 	setRegistrationSMSConfigForTest(true)
-	var deliveredCode string
 	sendIMVerificationCode = func(_ types.TenantID, recipient, _, scene, code string) error {
-		if recipient != "+8613800138000" || scene != "register" {
-			t.Fatalf("unexpected delivery: recipient=%q scene=%q", recipient, scene)
-		}
-		deliveredCode = code
+		t.Fatalf("registration SMS sender must not be called before SMS integration: recipient=%q scene=%q code=%q", recipient, scene, code)
 		return nil
 	}
 	defer func() {
@@ -1286,10 +1282,9 @@ func TestServeIMVerificationCodesCreatesChallenge(t *testing.T) {
 	if verifications.created.CodeHash == "" || strings.Contains(rec.Body.String(), verifications.created.CodeHash) {
 		t.Fatalf("code hash missing or leaked: %#v body=%s", verifications.created, rec.Body.String())
 	}
-	if len(deliveredCode) != imVerificationCodeLength ||
-		verifications.created.CodeHash != hashIMSecret(7, "register", verifications.created.ChallengeID,
-			verifications.created.PhoneHash, deliveredCode) {
-		t.Fatalf("stored challenge does not match delivered code %q", deliveredCode)
+	if verifications.created.CodeHash != hashIMSecret(7, "register", verifications.created.ChallengeID,
+		verifications.created.PhoneHash, "123456") {
+		t.Fatalf("stored challenge does not match fixed registration code")
 	}
 	resp := decodeIMHTTPResponse(t, rec)
 	data := resp.Data.(map[string]any)
@@ -1376,21 +1371,28 @@ func TestServeIMPasswordResetCodeFindsPhoneWithoutTelCredential(t *testing.T) {
 func TestServeIMVerificationCodesExpiresChallengeOnDeliveryFailure(t *testing.T) {
 	oldTenants := store.Tenants
 	oldVerifications := store.Verifications
+	oldUsers := store.Users
 	oldSender := sendIMVerificationCode
 	store.Tenants = testTenantStore{tenant: &types.Tenant{ID: 7, Code: "acme", State: types.TenantStateActive}}
 	verifications := &testVerificationStore{}
 	store.Verifications = verifications
 	setRegistrationSMSConfigForTest(true)
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+	users := mock_store.NewMockUsersPersistenceInterface(ctrl)
+	users.EXPECT().GetByPhone(types.TenantID(7), "+8613800138000").Return(types.Uid(42), nil)
+	store.Users = users
 	sendIMVerificationCode = func(_ types.TenantID, _, _, _, _ string) error { return types.ErrInternal }
 	defer func() {
 		store.Tenants = oldTenants
 		store.Verifications = oldVerifications
+		store.Users = oldUsers
 		sendIMVerificationCode = oldSender
 		resetRegistrationSMSConfigForTest()
 	}()
 
 	req := httptest.NewRequest(http.MethodPost, "/v1/im/auth/verification-codes",
-		bytes.NewBufferString(`{"scene":"register","phone":"+8613800138000"}`))
+		bytes.NewBufferString(`{"scene":"reset_password","phone":"+8613800138000"}`))
 	req.Header.Set("X-Tinode-APIKey", makeTestAPIKey(t))
 	req.Header.Set("X-Tenant-Code", "acme")
 	rec := httptest.NewRecorder()