What are the causes of WordPress admin-ajax.php 400 bad request

A “400 Bad Request” error related to admin-ajax.php in WordPress can be caused by various factors. Here are some common reasons for this issue:

  1. Plugin or Theme Conflict: Sometimes, a conflict between plugins or themes can lead to errors in the AJAX requests made to admin-ajax.php. If a plugin or theme is poorly coded or incompatible with your WordPress setup, it may result in a “400 Bad Request” error.
  2. Server Configuration: Server misconfigurations, such as incorrect server settings or limitations, can cause issues with AJAX requests. This may include limitations on request size, execution time, or memory allocation.
  3. Security Plugins or Firewall: Security plugins or server firewalls might block AJAX requests to admin-ajax.php if they perceive them as malicious. This can happen if the security measures are too strict or if there are false positives.
  4. Incorrect AJAX Implementation: Errors in the implementation of AJAX requests within your theme or plugin can lead to malformed requests, triggering a “400 Bad Request” response from the server.
  5. Large or Complex Requests: Sending large amounts of data or complex AJAX requests can sometimes exceed server limits or cause timeouts, resulting in a “400 Bad Request” error.
  6. Corrupted WordPress Core Files: In rare cases, corrupted or missing WordPress core files related to AJAX functionality can cause issues with admin-ajax.php requests.
  7. Resource Limitations: Your server may have resource limitations in place, such as memory limits or maximum execution time, which could cause AJAX requests to fail.

To troubleshoot and resolve this issue, you can try the following steps:

  • Deactivate plugins and switch to a default theme to identify if a plugin or theme is causing the conflict.
  • Check server error logs for more detailed information about the “400 Bad Request” error.
  • Review AJAX implementation code to ensure it’s correctly formatted and error-free.
  • Contact your web hosting provider to inquire about server configurations or limitations.
  • Consider temporarily disabling security plugins or firewalls to see if they’re blocking legitimate requests.
  • Ensure that your WordPress installation is up-to-date and that core files are intact and not corrupted.