What does "voucher code invalid or has not become available yet" mean on PlayStation?

Errors E-82000130 and WC-40372-6 both show the message "The voucher code you have entered is invalid or has not become available yet." This means either the code has a future activation date (check your card or order confirmation for a date), there's a typo (copy-paste instead of typing), the code is region-locked to a different account region, your account doesn't meet the voucher's conditions (age restriction, platform, or account type), the code has expired, or it was already used. Check your Transaction History in Account Management to confirm whether it was already redeemed.