Enable Full Invoice Payment Option When Payment Request is Active

Summary:
Add functionality to allow customers to pay the full invoice amount even when a Payment Request is active, which currently limits them to only paying the requested amount. This enhancement will give customers flexibility to pay more than the requested amount (up to the full balance) and will dynamically update payment button calculations including applicable fees.

User Story:
As a customer receiving an invoice with an active Payment Request, I want the option to pay the full remaining balance instead of being limited to only the requested payment amount, so that I can settle my entire invoice in one transaction if I prefer, rather than making multiple payments.