I've got a code for Beat Cop.
But i get "Uh oh. This code has expired. If you believe this is incorrect, please let us know. "
What can i do?
Can you check if this code is valid?
when it expired?

Since this looks indeed like a code from Amazon Prime Gaming, the code is expired (the offer was only viable for January 2023, and may even have been expired earlier (that is: before January 31st.), depending on what timeframe for redeeming the key was set).

Quote from Amazon: "The code can only be redeemed once and expires after the offer expires."

Edit: couldn't find the exact dates for "Beat Cop" in particular, but here's the timeframe for "the big" game in January:

Quote: "To claim The Evil Within 2, Amazon Prime subscribers simply need to redeem the offer, which is for PC only, and they'll be given a code that can be used on GOG.
This code may be claimed anytime between January 3 and February 1, with the timeframe for the code's redemption on GOG lasting until February 15.
Fans have plenty of time to claim it then, but it may be best to avoid putting it off."

So, assuming the same timeframe was set for "Beat Cop", your key has expired already somewhen between February 1st and February 15th.

You can always check whether a code is still valid by entering the code on the "redeem" page. If it is, it will tell you when it will expire. (Just make sure to click "cancel" it you don't intend to redeem the game right now, assuming it is valid.)
Also, many of GOG's on-site giveaways will allow you to claim a free copy of the game or bundle on offer even if you already own a copy; in this case, you would automatically get a gift code instead. The corresponding e-mail will include not only the serial code itself, but that code's expiration date.

Unfortunately, there is no direct way to tell when an expired gift code...expired. For codes gotten from sources like Prime Gaming, it's probably best to make a note somehow of when each code will expire (excepting those that you redeem immediately, of course).