Why we are getting the error - "Program/Area: contactUpdate.printEmailReceiptUpdateSubject: update(subscriptionSaveResults)Description: Object (id = xxxxxxxxxxxx) is currently in trigger AAkPay.contactUpd, therefore it cannot recursively update itself" ?
You may have another package that is interfering with the updates.
The latest version of Payments2Us from the AppExchange should include the package name in the error if that is causing the issue.
Alternatively, there might be a process builder, workflow or flow that is going triggering from the subscription that is updating the contact record. This might be causing a similar error to occur.
Regardless of the above, you can manual address, There are field calls "Email" and "Print Email Receipt" exist on the Contact and one called "Print Email Receipt" on the Subscription object.
Add these fields to the page layout. Edit the page layout and make the fields editable.
Then simply put the correct email address into all 3 fields (probably copying the Email to the two "print email receipt" fields).