Start with quick checks: check your site URL, login details, and server status....

https://wiki-fusion.win/index.php/WordPress_Database_Connection_Error_When_Using_Amazon_RDS

Start with quick checks: check your site URL, login details, and server status. If the error stays, try deeper fixes like table repair or WordPress settings. If the database is down or out of reach, contact your host and say when the issue began today.