For this error, you can refer to our API reference here. Based on that reference, there are 2 (two) versions of the customer endpoint.
- V1 version is 2020-05-19 version
- V2 version is 2020-10-31 version (v2 and default if no API version header is present).
If you encountered CUSTOMER_NOT_FOUND_ERROR, probably you are using the endpoint V2 version. Because currently, Direct Debit APIs only support customers from 2020-05-19 version.
So, if you got that error, we suggest you create customers using customer endpoint 2020-05-19 version