Add support for in3 payment method

[rvdsteege]

From customer:

De in3 betaalmethode is geselecteerd in Mollie, deze is ook voor een aantal formulieren in GravityForms te selecteren maar in Memberpress krijgen we helaas de payment gateway niet te zien.

Klopt het dat dit nog niet mogelijk is? Zo ja wanneer zou dit wel mogelijk zijn? Zo nee, kunnen jullie een oplossing geven hoe dit wel te integreren is in Memberpress?

Simply adding the in3 payment method to MemberPress currently results in the following gateway error message:

ERROR: Unprocessable Entity - The payment method does not support recurring type

If we don't set support for the subscription capabilities in MemberPress (like create-subscriptions) for a payment method, should we then still continue to try to add a subscription to the payment?

https://github.com/pronamic/wp-pronamic-pay-memberpress/blob/b5b6be195ea345698a97a895b25f6b67697ac9ef/src/Gateways/Gateway.php#L96-L119

https://github.com/pronamic/wp-pronamic-pay-memberpress/blob/b5b6be195ea345698a97a895b25f6b67697ac9ef/src/Pronamic.php#L123-L136

Internal Help Scout ticket: https://secure.helpscout.net/conversation/2275733463/25784

CC: @remcotolsma

[remcotolsma]

I think this is MemberPress territory and we have the next MemberPress issue open for that (not yet reported to MemberPress itself as far as I know):

• https://github.com/pronamic/memberpress/issues/2

If we don't set support for the subscription capabilities in MemberPress (like create-subscriptions) for a payment method, should we then still continue to try to add a subscription to the payment?

I think so, for recurring memberships we also want users/administrators to see the error message:

ERROR: Unprocessable Entity - The payment method does not support recurring type

[rvdsteege]

Ah, I think I missed the one-time membership option. in3 works fine in that case and the error message is indeed correct then for recurring memberships. I created PR #14 to add the in3 payment method.