If you’re finding JSON API requests back to your WordPress website fail Microsoft Internet Explorer, and you’ve got WP Super Cache installed, check you do not have Debugging enabled in the WP Super Cache Settings.

With Debugging enabled, WP Super Cache adds an extra HTML comment at the end of every page like this;

Page not cached by WP Super Cache. No closing HTML tag. Check your theme

Where this causes problems is the HTML comment is also added to the pages generated by the JSON API plugin, breaking the JSON file.

From what we can see, the addition of this debugging comment stops Internet Explorer IE11 (and possibly earlier Edge and older versions of IE) from being able to read the JSON data.

To fix,

  1. Log in to your WordPress Dashboard.
  2. Navigate to WP Super Cache (Settings > WP Super Cache.)
  3. Click the **Debug** tab.
  4. Uncheck *Debugging*
  5. Click **Save**