Hi I just purchased an apple gift card and when the code gets scan or I entered manually it gets me the same message

Chances are you entered one or more of the characters wrong. Please review the support article linked below for examples and instructions on redeeming your gift card. If none to the methods explained resolve your issue, please use the support links in the article to contact Apple Support.

If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support

The biggest problem is people confusing the letter O with the number 0. Make sure you are entering the correct one.