The device this was tested on is 4987_iPhone 6+_11.2
The live build didn't provide UE4 logging, but that will be added.
There is also a failure to purchase on Android but it gets farther than this; it occurs when the store attempts to charge the credit card, so that will be logged separately.
RESULT: "Failed to make purchase. Please try again."
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-63429 in the post.