You are getting Client Deactivated because these credentials are being used somewhere else, this could be because they swapped tills or replaced tills, etc.
Press Windows Key + R to open Run
Type regedit and press enter.
Navigate to the below root;
Computer\HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Remedy\EFTSRV\SERVER
Below the highlighted value needs to be deleted. Do Not Delete The Actual Key, just highlight the text below and press backspace or delete on your keyboard.
restart linkly server and the Server Should Go Green