Can't add a card via the user payment methods page

I have not implemented any 'stored payment method' functionality (and am currently not intending to since my own customer base doesn't need it).
I have just checked and the Gateway is inheriting from 'SupportsStoredPaymentMethodsInterface' so that's probably the issue.

I will need to refactor the inheritance slightly to remove 'SupportsStoredPaymentMethodsInterface' from the inheritance chain.

The issue is supporting creating payment methods 'off-checkout'. Opayo Pi supports it, Drupal Commerce supports it but this gateway doesn't currently implement it.

(It could be added but I suspect it's a fair chunk of work, which I won't have any time for in the foreseeable and I'm not getting the feeling anybody else is keen and available to jump in and add it.)

In an ideal world I would take out the inheritance of 'SupportsCreatingPaymentMethodsInterface' but it looks like that would probably break the existing normal checkout for this gateway.
I don't think Drupal Commerce has advanced yet to naturally support a payment process like Opayo Pi where most of the heavy lifting is
done between the customer's browser Javascript and the Opayo servers.

Instead I might add some code to identify and intercept when a customer tries to add a payment method 'off-checkout' (e.g. on the user's 'Payment Methods' tab) and display a nice 'Not available' or 'Not supported' message.

Thanks for the response, agreed we should at least display a prompt for this feature not been supported. Then this ticket can be put into backlog for when one of us has time to implement.

Also worth noting even if we're not saving its still registers in the db