"Get-Paid-To" (GPT) websites allow you to earn points that can be exchanged for official Google Play gift cards.
An outdated Play Store may lack the latest security protocols for code redemption. codigos gratis play store fix
There is no technical "fix" to get free Play Store codes illegitimately. Use the safe, legal methods above. If you have a real code that won't work, focus on the cache/country/account fixes listed. "Get-Paid-To" (GPT) websites allow you to earn points