WordPress: Ajax 400 error in console

Click on team member's image & a popup with more information is suppose to pop up. This has stopped working. I have attached an image of the people who you're supposed to be able to click on, & then further details about the person clicked on, then show up in a pop-up. This isn't working.

In the console, I get the following, every time one of the images is clicked on: POST http://localhost/englishfinal/wp-admin/admin-ajax.php 400 (Bad Request) .