Why did I get API error code 11451?
PayPal returned API error code 11451 - Billing Agreement ID or transaction ID is not valid.
Cause
The Reference ID field caused the error for one of the following reasons:
- The field is empty.
- It contains an invalid transaction.
- It isn't associated with a billing agreement.
- It can't be decrypted.
Solution
Check that the billing agreement ID is correct. If it is, inform the customer that a new billing agreement is needed and offer them the chance to sign up for a new billing agreement through Express Checkout.
Note: See the Developer Portal for a complete list of NVP/SOAP API error codes.