Redeem Store Gift Card

I received a Store Gift Card by email some time ago when I traded in my old iPad for a new one and now want to redeem it to help pay for a new phone. The card number doesn’t appear to fit the format that is described in all the comments/videos on the subject of redeeming. When I try to add it to my ApplePay Wallet i get the message “Safari cannot download this file”. The card number is an 18 digit number in the following format: xx xxxx xxxx xxxx xxxx

how can I resolve this?

thanks