mysqli_connect(): (HY000/1045): Access denied for user 'username'@'localhost' (using password: YES)

mysqli_connect(): (HY000/1045): Access denied for user 'username'@'localhost' (using password: YES)
The error message "mysqli_connect(): (HY000/1045): Access denied for user 'username'@'localhost' (using password: YES)" indicates that the PHP script is unable to connect to the MySQL database due to incorrect credentials or insufficient privileges.

Here are some possible causes and solutions for this error:

Incorrect Username or Password: Double-check the username and password you are using to connect to the database. Make sure they are correct and have the necessary permissions to access the database.

Database User Privileges: Ensure that the database user has the appropriate privileges to connect and access the database. Grant the necessary privileges to the user if needed.

Incorrect Hostname: If the MySQL server is running on a remote host, make sure you are using the correct hostname or IP address to connect. If it's on the same server, use 'localhost' as the hostname.

Firewall or IP Whitelisting: Check if there are any firewalls or IP whitelisting rules that may be blocking the connection to the MySQL server. Make sure the PHP server is allowed to connect to the MySQL server.

MySQL Server Configuration: Verify the MySQL server configuration to ensure it allows remote connections and is running properly.

Password Encryption: If the password is stored in a configuration file or environment variable, ensure it is not encrypted or hashed. The mysqli_connect() function expects the password to be in plain text.

Check MySQL Service: Make sure that the MySQL server is running and accessible.

MySQL Server Port: Check if the MySQL server is running on the default port (3306) or a different port. Specify the correct port in the connection string if needed.

To further troubleshoot the issue, you can try connecting to the MySQL server using a MySQL client like mysql command-line tool or a GUI tool like phpMyAdmin with the same credentials to verify if the login works correctly. If the issue persists, you might need to contact your hosting provider or server administrator for assistance in resolving the access issue.

Always remember to handle database credentials securely and avoid hardcoding sensitive information in your PHP scripts. Use environment variables or configuration files outside of the webroot to store sensitive data securely.