It doesnt actyally charge anything, any card should work. You can also enter any sample card number or 16 zeroes as credit card number.
I thought it was really funny to have it actually validate the number, but I do agree and I definitely should've added a button to just skip that bit.
I was indeed planning on adding some kind of "true ending" but I ran out of time since I had to catch a ferry and wouldn't have been able to upload the game :)