You cant make anymore payments as the Cakewalk Store is now closed.
On a personal note, I wouldn't make any more payments because you don't know what's going to happen from here on out and I would hate to suggest to you to make a payment.
As I believe, Cakewalk will announce an unlocking code, application, exc that will allow you to continue using the software. Please don't hold me to that, but that's my guess.