Your PSN account country decides which PlayStation card works. Here is how to check it.
PlayStation Store cards only work on accounts from the same country. A Saudi card works on a Saudi account, a UAE card on a UAE account, a US card on a US account. This is the most common reason a PSN code is refused.
Prices are different between stores. Some players keep a second account in another country for this reason. If you do, make sure the card matches that second account, and keep in mind that some content and online services may differ by region.
You cannot change the country of an existing PSN account. If you buy the wrong region, the code cannot be moved to your account.