Problem connecting to cpanel (Incorrect login details.)

Hi guys. I am having a problem with a cpanel account that is no longer accessible. At each connection. At the WHMCS level, I can connect to it automatically, and everything seems correct. Unfortunately the account owner is not an administrator. I am WHM Root and WHMCS Administrator. I thought it was IP address blocking, but it wasn't. At the WHM level, everything seems correct. and the logs show no errors. This problem even prevents connection with MySQL. Someone help me to solve this problem?