diff --git a/backend/handlers/payments/payments_test.go b/backend/handlers/payments/payments_test.go
index 111a5e9..651fc35 100644
--- a/backend/handlers/payments/payments_test.go
+++ b/backend/handlers/payments/payments_test.go
@@ -2153,24 +2153,10 @@ func TestCreatePaymentMethod_HappyPath(t *testing.T) {
 
 	w := makePaymentRequest(handler, "POST", "/api/user/payment-methods", reqBody, token, ctx)
 
-	if w.Code != http.StatusOK {
-		t.Errorf("expected status 200, got %d. body: %s", w.Code, w.Body.String())
-		return
-	}
-
-	var card SavedCard
-	if err := json.Unmarshal(w.Body.Bytes(), &card); err != nil {
-		t.Fatalf("failed to parse response: %v", err)
-	}
-
-	if card.Brand != "VISA" {
-		t.Errorf("expected brand VISA, got %s", card.Brand)
-	}
-	if card.Last4 != "1111" {
-		t.Errorf("expected last4 1111, got %s", card.Last4)
-	}
-	if !card.IsDefault {
-		t.Error("expected first card to be default")
+	// PCI-DSS parity: raw PAN card creation is blocked in production, so the
+	// mock must reject it too — otherwise dev testing masks a prod failure.
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected status 500 (raw PAN rejected), got %d. body: %s", w.Code, w.Body.String())
 	}
 }
 
@@ -2296,7 +2282,8 @@ func TestCreatePaymentMethod_SecondCardNotDefault(t *testing.T) {
 
 	token := jwt.GenerateUserToken(userID)
 
-	// Create first card
+	// PCI-DSS parity: raw PAN card creation is blocked in production, so the
+	// mock must reject it too — otherwise dev testing masks a prod failure.
 	handler := CreatePaymentMethod
 	reqBody := CreatePaymentMethodRequest{
 		CardNumber: "4111111111111111",
@@ -2305,31 +2292,8 @@ func TestCreatePaymentMethod_SecondCardNotDefault(t *testing.T) {
 	}
 
 	w := makePaymentRequest(handler, "POST", "/api/user/payment-methods", reqBody, token, ctx)
-	if w.Code != http.StatusOK {
-		t.Fatalf("failed to create first card: %d. body: %s", w.Code, w.Body.String())
-	}
-
-	reqBody2 := CreatePaymentMethodRequest{
-		CardNumber: "5500000000000004",
-		Expiry:     "06/30",
-		CVC:        "456",
-	}
-
-	w = makePaymentRequest(handler, "POST", "/api/user/payment-methods", reqBody2, token, ctx)
-	if w.Code != http.StatusOK {
-		t.Fatalf("failed to create second card: %d. body: %s", w.Code, w.Body.String())
-	}
-
-	var card SavedCard
-	if err := json.Unmarshal(w.Body.Bytes(), &card); err != nil {
-		t.Fatalf("failed to parse response: %v", err)
-	}
-
-	if card.Brand != "MASTERCARD" {
-		t.Errorf("expected brand MASTERCARD, got %s", card.Brand)
-	}
-	if card.IsDefault {
-		t.Error("expected second card to NOT be default")
+	if w.Code != http.StatusInternalServerError {
+		t.Fatalf("expected 500 (raw PAN rejected), got %d. body: %s", w.Code, w.Body.String())
 	}
 }
 
diff --git a/backend/internal/square/square_dev.go b/backend/internal/square/square_dev.go
index 695b4d0..67f1525 100644
--- a/backend/internal/square/square_dev.go
+++ b/backend/internal/square/square_dev.go
@@ -320,32 +320,11 @@ func (m *MockClient) RefundPayment(ctx context.Context, req RefundPaymentReq) (*
 func (m *MockClient) CreateCardOnFile(ctx context.Context, userID, cardToken string) (*CardOnFile, error) {
 	log.Printf("[SQUARE-MOCK] CreateCardOnFile: user=%s", userID)
 
-	// Detect card info from the input token.
-	// Raw card numbers (digit-only, possibly with spaces) are parsed directly.
-	// Nonce-like tokens (cnon:xxx etc.) use detectCardInfo for mapped values.
-	cleanDigits := strings.ReplaceAll(cardToken, " ", "")
-	cardBrand := "VISA"
-	cardLast4 := "4242"
-	cardExpMonth := 12
-	cardExpYear := 2030
-
-	if isAllDigits(cleanDigits) && len(cleanDigits) >= 13 {
-		cardLast4 = cleanDigits[len(cleanDigits)-4:]
-		firstDigit := string(cleanDigits[0])
-		switch firstDigit {
-		case "4":
-			cardBrand = "VISA"
-		case "5":
-			cardBrand = "MASTERCARD"
-		case "3":
-			cardBrand = "AMERICAN_EXPRESS"
-		case "6":
-			cardBrand = "DISCOVER"
-		}
-	} else {
-		brand, last4 := detectCardInfo(cardToken)
-		cardBrand = brand
-		cardLast4 = last4
+	// Match the real Square API: source_id must be a token (cnon:xxx nonce or
+	// ccof:xxx card ID). Raw PANs are rejected exactly as Square would, so the
+	// mock behaves identically to production.
+	if !isTokenLike(cardToken) {
+		return nil, fmt.Errorf("invalid source_id: %q — use a card nonce (cnon:xxx) or card ID (ccof:xxx)", cardToken)
 	}
 
 	m.mu.Lock()
@@ -357,13 +336,14 @@ func (m *MockClient) CreateCardOnFile(ctx context.Context, userID, cardToken str
 
 	now := clock.Now().UTC()
 	cardID := fmt.Sprintf("mock_card_%d", now.UnixNano())
+	brand, last4 := detectCardInfo(cardToken)
 	card := &CardOnFile{
 		ID:             cardID,
 		CardID:         fmt.Sprintf("ccof_mock_%d", now.UnixNano()),
-		Brand:          cardBrand,
-		Last4:          cardLast4,
-		ExpMonth:       cardExpMonth,
-		ExpYear:        cardExpYear,
+		Brand:          brand,
+		Last4:          last4,
+		ExpMonth:       12,
+		ExpYear:        2030,
 		Fingerprint:    fmt.Sprintf("sqfp_mock_%d", now.UnixNano()),
 		CardholderName: "John Doe",
 		CustomerID:     userID,
@@ -378,46 +358,10 @@ func (m *MockClient) CreateCardOnFile(ctx context.Context, userID, cardToken str
 }
 
 func (m *MockClient) CreateCardOnFileRaw(ctx context.Context, userID, cardNumber string, expMonth, expYear int, cvc string) (*CardOnFile, error) {
-	log.Printf("[SQUARE-MOCK] CreateCardOnFileRaw: user=%s", userID)
-
-	if len(cardNumber) < 4 {
-		return nil, fmt.Errorf("invalid card number: too short")
-	}
-
-	m.mu.Lock()
-	defer m.mu.Unlock()
-
-	if m.cards[userID] == nil {
-		m.cards[userID] = make(map[string]*CardOnFile)
-	}
-
-	now := clock.Now().UTC()
-	cardID := fmt.Sprintf("mock_card_%d", now.UnixNano())
-	last4 := cardNumber[len(cardNumber)-4:]
-	brands := map[string]string{"4": "VISA", "5": "MASTERCARD", "3": "AMERICAN_EXPRESS", "6": "DISCOVER"}
-	brand := brands[string(cardNumber[0])]
-	if brand == "" {
-		brand = "UNKNOWN"
-	}
-
-	card := &CardOnFile{
-		ID:             cardID,
-		CardID:         fmt.Sprintf("ccof_mock_%d", now.UnixNano()),
-		Brand:          brand,
-		Last4:          last4,
-		ExpMonth:       expMonth,
-		ExpYear:        expYear,
-		Fingerprint:    fmt.Sprintf("sqfp_mock_%d", now.UnixNano()),
-		CardholderName: "John Doe",
-		CustomerID:     userID,
-		Enabled:        true,
-		IsDefault:      len(m.cards[userID]) == 0,
-		Version:        1,
-		CreatedAt:      now.Format(time.RFC3339),
-	}
-	m.cards[userID][cardID] = card
-	log.Printf("[SQUARE-MOCK] Card created: id=%s, brand=%s, last4=%s", cardID, card.Brand, card.Last4)
-	return card, nil
+	// PCI-DSS parity with production: raw card numbers are never accepted.
+	// The mock must behave identically to the ProdClient so dev testing does
+	// not mask a production failure.
+	return nil, fmt.Errorf("square: raw card number input is not supported in production — use CreateCardOnFile with a card nonce")
 }
 
 func (m *MockClient) GetCardsOnFile(ctx context.Context, userID string) ([]CardOnFile, error) {
@@ -454,14 +398,10 @@ func (m *MockClient) DeleteCardOnFile(ctx context.Context, cardID string) error
 	return fmt.Errorf("card not found: %s", cardID)
 }
 
-// isAllDigits returns true if every rune in s is an ASCII digit.
-func isAllDigits(s string) bool {
-	for _, r := range s {
-		if r < '0' || r > '9' {
-			return false
-		}
-	}
-	return len(s) > 0
+// isTokenLike returns true for Square source_id tokens: cnon:xxx nonces and
+// ccof:xxx card IDs. Raw PANs (all digits) are NOT token-like and are rejected.
+func isTokenLike(s string) bool {
+	return strings.HasPrefix(s, "cnon:") || strings.HasPrefix(s, "ccof:")
 }
 
 func realBaseURL(env string) string {
diff --git a/backend/internal/square/square_dev_test.go b/backend/internal/square/square_dev_test.go
index 2b6065a..151868e 100644
--- a/backend/internal/square/square_dev_test.go
+++ b/backend/internal/square/square_dev_test.go
@@ -237,79 +237,32 @@ func TestDevClient_GetCheckout_NotFound(t *testing.T) {
 	require.Error(t, err)
 }
 
-func TestDevClient_CreateCardOnFileRaw_Visa(t *testing.T) {
-	client := NewDevClient().(*MockClient)
-	card, err := client.CreateCardOnFileRaw(context.Background(), "user-raw-1", "4111111111111111", 12, 2030, "123")
-	require.NoError(t, err)
-	assert.Equal(t, "VISA", card.Brand)
-	assert.Equal(t, "1111", card.Last4)
-	assert.True(t, card.IsDefault)
-	assert.True(t, card.Enabled)
-	assert.Equal(t, 12, card.ExpMonth)
-	assert.Equal(t, 2030, card.ExpYear)
-	assert.NotEmpty(t, card.CreatedAt)
-	assert.Greater(t, card.Version, int64(0))
-}
-
-func TestDevClient_CreateCardOnFileRaw_Mastercard(t *testing.T) {
+func TestDevClient_CreateCardOnFileRaw_Rejected_ProdParity(t *testing.T) {
+	// PCI-DSS parity: the mock must reject raw PANs exactly like the
+	// ProdClient, so dev testing cannot mask a production failure.
 	client := NewDevClient().(*MockClient)
 	ctx := context.Background()
-	// First card to set up non-default check
-	_, err := client.CreateCardOnFileRaw(ctx, "user-raw-2", "4111111111111111", 12, 2030, "123")
-	require.NoError(t, err)
-	// Mastercard is second → not default
-	card, err := client.CreateCardOnFileRaw(ctx, "user-raw-2", "5555555555554444", 12, 2030, "123")
-	require.NoError(t, err)
-	assert.Equal(t, "MASTERCARD", card.Brand)
-	assert.Equal(t, "4444", card.Last4)
-	assert.False(t, card.IsDefault)
-	assert.True(t, card.Enabled)
-	assert.Equal(t, 12, card.ExpMonth)
-	assert.Equal(t, 2030, card.ExpYear)
-	assert.NotEmpty(t, card.CreatedAt)
-	assert.Greater(t, card.Version, int64(0))
-}
 
-func TestDevClient_CreateCardOnFileRaw_Amex(t *testing.T) {
-	client := NewDevClient().(*MockClient)
-	card, err := client.CreateCardOnFileRaw(context.Background(), "user-raw-3", "378282246310005", 12, 2030, "123")
-	require.NoError(t, err)
-	assert.Equal(t, "AMERICAN_EXPRESS", card.Brand)
-	assert.Equal(t, "0005", card.Last4)
-	assert.True(t, card.IsDefault)
-	assert.True(t, card.Enabled)
-	assert.Equal(t, 12, card.ExpMonth)
-	assert.Equal(t, 2030, card.ExpYear)
-	assert.NotEmpty(t, card.CreatedAt)
-	assert.Greater(t, card.Version, int64(0))
-}
+	tests := []struct {
+		name       string
+		cardNumber string
+	}{
+		{"visa", "4111111111111111"},
+		{"mastercard", "5555555555554444"},
+		{"amex", "378282246310005"},
+		{"discover", "6011111111111117"},
+		{"unknown brand", "9999999999999999"},
+		{"too short", "123"},
+	}
 
-func TestDevClient_CreateCardOnFileRaw_Discover(t *testing.T) {
-	client := NewDevClient().(*MockClient)
-	card, err := client.CreateCardOnFileRaw(context.Background(), "user-raw-4", "6011111111111117", 12, 2030, "123")
-	require.NoError(t, err)
-	assert.Equal(t, "DISCOVER", card.Brand)
-	assert.Equal(t, "1117", card.Last4)
-	assert.True(t, card.IsDefault)
-	assert.True(t, card.Enabled)
-	assert.Equal(t, 12, card.ExpMonth)
-	assert.Equal(t, 2030, card.ExpYear)
-	assert.NotEmpty(t, card.CreatedAt)
-	assert.Greater(t, card.Version, int64(0))
-}
-
-func TestDevClient_CreateCardOnFileRaw_UnknownBrand(t *testing.T) {
-	client := NewDevClient().(*MockClient)
-	card, err := client.CreateCardOnFileRaw(context.Background(), "user-raw-5", "9999999999999999", 12, 2030, "123")
-	require.NoError(t, err)
-	assert.Equal(t, "UNKNOWN", card.Brand)
-	assert.Equal(t, "9999", card.Last4)
-	assert.True(t, card.IsDefault)
-	assert.True(t, card.Enabled)
-	assert.Equal(t, 12, card.ExpMonth)
-	assert.Equal(t, 2030, card.ExpYear)
-	assert.NotEmpty(t, card.CreatedAt)
-	assert.Greater(t, card.Version, int64(0))
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			card, err := client.CreateCardOnFileRaw(ctx, "user-raw-"+tt.name, tt.cardNumber, 12, 2030, "123")
+			require.Error(t, err, "raw PAN must be rejected for production parity")
+			assert.Nil(t, card)
+			assert.Contains(t, err.Error(), "raw card number input is not supported")
+		})
+	}
 }
 
 func TestCreatePayment_ShouldFail(t *testing.T) {
@@ -479,40 +432,31 @@ func TestDevClient_CreateCardOnFileRaw_WithBrandDetection(t *testing.T) {
 	userID := "user-raw-brand-detect"
 
 	card, err := client.CreateCardOnFileRaw(ctx, userID, "4111111111111111", 12, 2030, "123")
-	require.NoError(t, err)
-	assert.Equal(t, "VISA", card.Brand)
-	assert.Equal(t, "1111", card.Last4)
-	assert.True(t, card.Enabled)
-	assert.Equal(t, 12, card.ExpMonth)
-	assert.Equal(t, 2030, card.ExpYear)
+	require.Error(t, err, "raw PAN must be rejected for production parity")
+	assert.Nil(t, card)
 }
 
-func TestDevClient_CreateCardOnFile_RawNumber(t *testing.T) {
+func TestDevClient_CreateCardOnFile_RejectsRawPAN(t *testing.T) {
 	client := NewDevClient().(*MockClient)
 	ctx := context.Background()
 
 	tests := []struct {
-		name     string
-		cardNum  string
-		wantBrand string
-		wantLast4 string
+		name    string
+		cardNum string
 	}{
-		{"visa formatted", "4111 1111 1111 1111", "VISA", "1111"},
-		{"visa raw", "4111111111111111", "VISA", "1111"},
-		{"mastercard", "5500 0000 0000 0004", "MASTERCARD", "0004"},
-		{"amex", "3400 0000 0000 009", "AMERICAN_EXPRESS", "0009"},
-		{"discover", "6011 0000 0000 0004", "DISCOVER", "0004"},
+		{"visa formatted", "4111 1111 1111 1111"},
+		{"visa raw", "4111111111111111"},
+		{"mastercard", "5500 0000 0000 0004"},
+		{"amex", "3400 0000 0000 009"},
+		{"discover", "6011 0000 0000 0004"},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			userID := fmt.Sprintf("user-raw-card-%s", tt.name)
 			card, err := client.CreateCardOnFile(ctx, userID, tt.cardNum)
-			require.NoError(t, err)
-			assert.Equal(t, tt.wantBrand, card.Brand)
-			assert.Equal(t, tt.wantLast4, card.Last4)
-			assert.True(t, card.Enabled)
-			assert.NotEmpty(t, card.CardholderName)
+			require.Error(t, err, "raw PAN must be rejected for production parity")
+			assert.Nil(t, card)
 		})
 	}
 }
@@ -540,7 +484,7 @@ func TestDevClient_CreateCardOnFileRaw_TooShort(t *testing.T) {
 
 	_, err := client.CreateCardOnFileRaw(ctx, "user-too-short", "123", 12, 2030, "999")
 	require.Error(t, err)
-	assert.Contains(t, err.Error(), "too short")
+	assert.Contains(t, err.Error(), "raw card number input is not supported")
 }
 
 func TestDevClient_GetCardsOnFile_Empty(t *testing.T) {