Verify the username and password: Make sure that you are entering the correct username and password for your OpenVPN connection. Check for any typos or case sensitivity issues.

Confirm the authentication method: OpenVPN supports various authentication methods, such as username/password, certificates, or both. Ensure that you are using the correct authentication method expected by the server. If certificates are required, ensure that you have the appropriate client certificate and key files.

Check the server-side configuration: The OpenVPN server configuration should match the authentication method you are using. Review the server configuration file (typically named server.conf) and ensure that the authentication settings are correctly configured.

Verify firewall or network restrictions: Sometimes, network firewalls or security policies can interfere with the authentication process. Ensure that the necessary ports and protocols (usually UDP port 1194 or TCP port 443) are allowed through any firewalls or routers between the client and server.

Check log files: Examine the OpenVPN log files on both the client and server sides to gather more information about the authentication failure. The log files can provide specific error messages or details that might help identify the cause of the issue.

Test with different clients: If possible, try connecting from different OpenVPN clients (e.g., official OpenVPN client, third-party clients) to see if the issue persists across multiple client applications.