The first thing to do before attempting any solutions is to check out Riot’s server status page to see if “Valorant” is suffering any outages. There’s nothing to do but wait if the game itself is down, after all, and this could save you the trouble of needlessly trying to fix your game client. The second important step would be to check your own internet connectivity — while doing a quick reset of your router just to be sure — and double-checking that your ID and password are correct.
If it seems you’re reliably connected to the internet, your credentials are input correctly, and the game servers are online, then it’s time to start looking into the solutions to your login issues. Riot provides a list of all the possible error codes and what they mean, along with some basic fixes that mostly involve restarting the game client and/or your PC. Some errors have to do with your account status and need a support ticket submission to be resolved — track down your error code to figure out what the cause of your issue is and try applying the suggested solution.