I bought RDR2 1 hour ago but the product code says the continuity is incorrect on Steam. If anyone has any information about this issue, can you help me?
Without checking, my guess is that you bought a code for RDR2 on Rockstar's client (or on Epic Games client) -not- Steam.
If you want it on Steam you need to buy it on Steam, same thing with Ubisoft and EA games.
I just checked and it's mentioned on the store page for the game.
To activate your game please visit: https://socialclub.rockstargames.com/games/activate/index-signin
You will need to sign in with a valid Social Club Account to activate your Rockstar Code or download a PC game client. If you don't have an account, you will need to create one.