Seeing this error?
FIELD_CUSTOM_VALIDATION_EXCEPTION: Profile is used by a Recurring Invoice, Account/Contact cannot be updated
This can happen when the Contact on the Payment Profile being created is different from the Contact on an existing active Recurring Invoice.
How to resolve it
The Contact on the Recurring Invoice and its associated Payment Profile must match.
If you don't want to specify a Contact, you can also leave the Contact field blank on either the Recurring Invoice or the Payment Profile.