If a payment_transaction_id is NOT provided, copy it from the subscription_transaction_id if available

[ideadude]

A customer had an issue where subscriptions were not synced due to the payment_transaction_id being blank. In reality, gateways will link up on the subscription_transaction_id. Making sure the payment id is not blank might help in some cases that check for it.

[kimcoleman]

We're considering this update but is it really still happening?

This is kind of hacky, and while there is limited downside maybe not needed.

There's a workaround, if you run into this error, you can duplicate the membership_subscription_transaction_id column in your import (with the heading membership_payment_transaction_id).