Most common reasons are:
- Code has been entered incorrectly.
- The code you are trying to redeem has expired or is not active yet.
- Your PlayStation™Network account region does not match the voucher's region.
- Your account does not meet the condition that the voucher is limited to.
- Make sure that the code is entered correctly.
- Check if the code's date is valid, and also check if the voucher has any restrictions of usage.