I like to think i'm pretty good with computers, but the way the process works is just so terrible convoluted. I mean you need to have a paladins account, then you sign up for twitch prime and then sign up for a free trial of Amazon prime. Then you gotta link it all to your paladins account and click claim/link from a few different places.. It's a madhouse.
I just used my bank card with no money on it to set up the account. Although I'm Canadian and pretty much every bank card now is viable as a pay-pal visa thinger.
I recommend you just keep trying and click on shit and being patient lol. It should work eventually once you jump through all the hoops.