I currently use wpadverts plugin and wants to limit the submission to 10 submit / month.

How can I do that?

I think I need to make a new row like "form_submissions" in "wp_usermeta" and store every time when the user submitted the form and make a cron task to delete the row value after a month.

And I need to query the row value on the form submit page like this:

    $result = mysqli_query($connect, "SELECT COUNT(*) AS `form_submission` FROM wp_usermeta");
    
        $row = mysqli_fetch_assoc($result);
    
        if($row['form_submission'] > 10) {
            // can't submit the form because you already have 10 post
        } else {
            // you can submit the form
        }
Or I'm totally lost? Sorry for my bad english.