Cannot change a password for MSSQL via Plesk > Tools & Settings > Database Servers > .MSSQLSERVER20** > Settings > Authentication due to the following error:
PLESK_ERROR: The test connection to the database server has failed because of an unacceptable password
Strict password requirements/policies.
Connect to the server via RDP
Open Command Prompt as Administrator and execute the following command to open SQL Server Management Studio:
Go to SQL Server Management Studio > Security > Logins > Administrator > Properties
Disable Enforce password policy and Enforce password expiration
Change a password for MSSQL via Plesk > Tools & Settings > Database Servers > .MSSQLSERVER20** > Settings > Authentication again
If the issue still persists, set Minimum password length on a Windows level to 10:
This requirement should be met by the password for MSSQL server.