Hey, howdy hey, Vivian. Thanks for visiting planDisney. As a 
Magic Key holder, you are among the most experienced of Disneyland guests, so I'm glad you trusted us with your question!
Purchasing discounted Disney gift cards is one of my favorite ways to maximize my savings on Disneyland resort merchandise, tickets, and food. You can certainly use Disney gift cards to pay off your Magic Key balance, but you will need to visit the ticket booth at the 
Disneyland Resort and do so in person. Unfortunately, there is currently no way to make additional Magic Key payments online, whether you use gift cards or a credit card. I hope this answers your question, Vivian!
I know as a Magic Key holder, you are amongst the most in-the-know Disneyland Guests, but be sure to check out the 
Disney Parks Blog and follow the 
Disneyland Magic Key Instagram for the most up-to-date information. With 
Halloween Time ending soon and 
snow on the horizon, you will want to see what fun goodies and experiences will be at the Happiest Place on Earth for the Holidays.
Vivian, thanks again for stopping by. I hope you will 
visit us again someday!
See you in the parks,
Melissa