This error may be displayed while you are trying to install any script like WordPress or any Auto installer script.
Solution ->
Check -> Database username and password:
**Login to PHPMyAdmin using your username & password (See: How to create Database user in PHPMyAdmin server). If there is an error that means either the database username and password is wrong or those credentials do not exist on the server. If you are using a live server like Cpanel, please see this reference: How to create a database username and add to the database | How to modify username, password.
Check -> Database name:
**Login to PHPMyAdmin -> Ensure that the target Database name exists in the Database list. If not exists then create a new Database with your preferred name (See: How to create Database in PHPMyAdmin server).
After these checks ensure that you are providing correct credentials in the input fields of the script installer.
(--Do not give space in between those credentials or as prefix and suffix.)
