If the form submission is failing with an “Ajax error”, there can be a number of different reasons for this. The error means that the request to submit the form failed. Either there was an error with the request, an error on the server while processing the form, or an invalid response sent back to the client.
Solution #1 – Known issues
Check if the site is using any plugin listed on the Known issues page, and implement the relevant fix described on that page.
Solution #2 – Plugin/theme conflict
If possible, follow this method to check for a conflict with another plugin or the theme.
Solution #3 – Check the logs to find the error message
Check the PHP error log and web server error log to see if there is a log entry at the time that the Ajax error occurs. For instance, if there was a PHP Fatal error, this would be logged to the PHP error log and the stack trace in the log entry should help track down the actual cause of the error. The web server error log may have an entry if the request is being blocked by, for example, ModSecurity. If you don’t know how to access these log files, your host should be able to help you with this.
If PHP error logging is not enabled on the site, you can temporarily enable debug logging, then submit the form to trigger the Ajax error, then check the /wp-content/debug.log file for an error message.
Solution #4 – Inspect the request in the browser
Open the browser developer tools by pressing F12 or Ctrl+Shift+I (Windows/Linux) or Command+Option+I (macOS), and go to the Network tab. Submit the form again, a new request should appear in the log. Click on the request and go to the Preview and Response tabs to look for an error message.
Solution #5 – Try the form in an incognito/private window
This should help rule out any issues with being logged into the site, and with browser extensions.
Solution #6 – Disable custom code (temporarily)
If you have any custom code that is hooked into Quform, try removing/disabling the code to see if it fixes the error.