即使PHP和JS文件独立工作，AJAX Call也无法正常工作

I've got an AJAX call set up. I've tested the JS file by alerting out the POST values I'm sending (and even alerting out the POST data string) and everything looks fine. I then take those values and put them in the PHP file where they are needed. I'm trying to replicate the process as easy as possible without any variables. It works fine. I then try to run the AJAX function and it gives me the error message. Here is my JS code (I declare the page_number and type variables earlier but it's not relevant; I've alerted those out and the variables are being assigned correctly):I've got an AJAX call set up. I've tested the J