I recently had a problem with a form submitted in WordPress returning a 404 error everytime even though it was submitting to an entirely valid URL. The form submission was managed via AJAX using jQuery.post(), so at first I assumed it was a Javascript problem – after a bit of testing, however, I discovered it was happening even if I submitted the form via PHP. I was entirely baffled by the issue (particularly because I had another form on the same site that submitted with no issues whatsoever) and spent a number of days trying to work it out – eventually I discovered the problem had nothing to do with Javascript, PHP or the server configuration, but was actually due to a restriction built into WordPress that isn’t immediately apparent.
It turns out that WordPress has a number of query variable names that are reserved for specific functions and cannot be used by any custom form on the site. In my case, I had a field called ‘name’ that was the culprit and simply changing it to ‘clientname’ fixed my problem entirely. The problem is that instead of giving a helpful error, WordPress just returns a 404 with no explanation about what went wrong or why it happened – even with debug mode on there is nothing helpful. This, as you can imagine, is particularly frustrating.
I haven’t found any official documentation listing the reserved variables, but there is this user-created page in the WordPress Codex that has a list of them (based on the variables used by WP_Query). I’m not sure how complete it is, but it seems fairly comprehensive.
Seeing as though I struggled with this for a few days, I thought I would share the solution here to help anyone else who might be having a similar issue.
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