How do I resolve a mysqli error in my PHP project?

It sounds like you might not have the mysqli extension enabled in your PHP configuration. Have you checked your php.ini file to ensure that the line `extension=mysqli` is not commented out? If it is, just remove the semicolon at the beginning of the line and restart your server.

You should double-check what the error message states. It’s important to have the exact message because it can provide clues on what’s wrong. Also, consider using PDO instead of mysqli for a more modern approach to database handling. It's generally preferred these days.

If you are unable to see the specific error details, that might be an issue with display_errors being disabled. You can enable it in your php.ini file like this: `display_errors = On` which will show you any errors you're hitting. Also, make sure that your mysqli extension is properly installed.