Errors

Scan to PayKit reports failures in two layers: the delegate callback that fired (e.g. scanToPayError(_:) vs scanToPayPaymentFailed(...)) and, for the error callback specifically, the MPError enum value passed in.

Delegate callbacks vs MPError

Layer	Where it shows up	How to read it
Delegate method	Which `MPScanToPayDelegate` method the SDK called	Tells you what kind of outcome occurred
`MPError` enum	The argument passed to `scanToPayError(_:)`	Tells you the specific cause

If scanToPayError(_:) fires, you'll have an MPError to inspect. For the other callbacks (success, failure, cancel, invalid code, registered, wallet completed), no MPError is involved.

MPScanToPayDelegate callbacks

Callback	When you'll see it
`scanToPayPaymentSucceeded(withTransactionReference:)`	Customer completed payment (verify server-side)
`scanToPayPaymentFailed(withTransactionReference:)`	Payment was attempted but failed (bank declined, etc.)
`scanToPayUserDidCancel()`	Customer aborted before completing
`scanToPayInvalidCode()`	`code` parameter was malformed, expired, or already used
`scanToPayError(_:)`	An error occurred — see MPError below
`scanToPayUserRegistered()`	Pre-registration completed
`scanToPayUserCompletedWallet()`	Manage-card flow completed

MPError enum

typedef NS_ENUM(NSInteger, MPError) {
    MPErrorNetworkError,
    MPErrorExceptionOccurred,
    MPErrorPaymentError,
    MPErrorOTPError,
    MPErrorInvalidCodeParameter,
    MPErrorInvalidApiKeyParameter,
    MPErrorSecureCodeNotSupported
};

Case	Description	What to do
`MPErrorNetworkError`	The SDK couldn't reach the platform	Show a "no network" message; let the customer retry
`MPErrorExceptionOccurred`	An unexpected internal exception	Raise a support ticket with details (capture timestamp)
`MPErrorPaymentError`	Payment-time error not surfaced as `scanToPayPaymentFailed`	Treat like `scanToPayPaymentFailed`; let the customer retry
`MPErrorOTPError`	OTP retrieval / validation failed during card registration	Customer can re-request the OTP
`MPErrorInvalidCodeParameter`	`code` parameter was missing or empty	Fix the calling code — `code` is mandatory
`MPErrorInvalidApiKeyParameter`	`apiKey` parameter was missing or invalid	Generate a fresh key in the Portal; verify the system (`.live` vs `.test`)
`MPErrorSecureCodeNotSupported`	The card's BIN requires 3D Secure but isn't enabled for it	Customer needs a different card, or the BIN config needs platform support

Triage cheat sheet

delegate callback?
├── scanToPayPaymentSucceeded(...)   → verify on backend, fulfil order
├── scanToPayPaymentFailed(...)      → log reference, retry option
├── scanToPayUserDidCancel()         → noop or analytics
├── scanToPayInvalidCode()           → bug in your code-creation flow
├── scanToPayUserRegistered()        → onboarding complete
├── scanToPayUserCompletedWallet()   → manage flow done
└── scanToPayError(MPError)
                    ├── .networkError              → retry, friendly message
                    ├── .exceptionOccurred         → support ticket
                    ├── .paymentError              → retry payment
                    ├── .otpError                  → retry OTP
                    ├── .invalidCodeParameter      → integration bug
                    ├── .invalidApiKeyParameter    → integration bug
                    └── .secureCodeNotSupported    → unsupported card

What's next

Test cards that produce specific errors → Sandbox and test cards
Confirm a transaction's true outcome → Webhooks / Querying transactions
Bank decline codes (when scanToPayPaymentFailed) → ISO response codes
Support escalation → Support