I'm staying away from the
MDE app for all reservation booking, it's been nothing but buggy and flaky, no payment declines like you experience but general errors when booking reservations.
It bit me a few weeks ago by dying at the last step of the process while booking Victoria and Albert's reservations, one at 5:30, another at 5:45, and another at 6:15 causing them to be in limbo until later that evening when they were kicked back into the system. Luckily the great folks at the Victoria and Albert's reservation line were watching and gave me a call when they saw the reservations become available to book.
It amazes me how flaky the main WDW website can be especially at peak booking times. You'd think it'd be adequately load tested and resourced accordingly for peak booking times especially for such fundamental functionality as reservation booking. I'm sick of seeing Donald and Stitch pop up when I'm in the middle of doing random things within the site. Perhaps instead of investing in clever error handling screen designs they could focus on the performance and stability of the site instead. I bet the problem is that HP is their "Official Technology Provider" nothing I've encountered from HP has been at a level of quality that a company/enterprise like Disney requires for what their standards for operational excellence in IT products and services should be.
One thing of mention is that the
Shop Disney Parks App has worked great compared to the rest of their apps/websites. Then again I've used it very infrequently and I don't have to ship or bill to a P.O. Box (which still doesn't work)
I use the MDE logo as my avatar because of how awesome I think it is as an overall concept of MDE, magic bands and My Magic +, and online checkin, have worked together flawlessly for me while in the parks, even when I was in the testing phase when it first came out (also because I think it matches with the styling of this forum very well

). However, when the main interfaces to book reservations are unreliable the whole thing kind of falls apart.
End rant.