What works for me is to google My Disney Experience and I get to this Disney page:
https://disneyworld.disney.go.com/plan/my-disney-experience/
You sign in. At the top of the page, on the far right, it says "My Disney Experience" with a pull-down menu. Under "Plan and Manage," select "My Reservations and Tickets." Your Hotel Reservations, Ticket info, Dining Reservations and Memory Maker info will show up (give it a few moments to load). Under your Hotel Reservation, if you have a balance, there is a button to push to make a payment. Press that button for payment choices. You will receive an email confirmation of payment made and updated balance due (if any).