I had the same problem with the build 14291 and the only way i could solve it was to reset the phone to an older build (10.0.10586.63 this one was for my Lumia 950). I used Windows device recovery tool. I made the purchase and then upgrade again and everything works fine.
In my case, the credit card was expired, I added a new method, I even tried to use PayPal, but it was the same error again and again.
Will I loose everything when I reset my Lumia 950 to an older build? I can only buy paid apps in the Store, but In App Purchase does not work at all. Very weird and a big problem! I hope there is another solution.