Stuck at Creating an AJAX Call based on this article https://premium.wpmudev.org/blog/load-posts-aja

Hello,

I'm trying to replicate this AJAX article tutorial. https://premium.wpmudev.org/blog/load-posts-ajax/

The thing is under Creating an AJAX Call, I don't see the alert 0 message. When I check console, this error came up.

POST https://iceiceicy.com/wingwah/wp-admin/admin-ajax.php 400 ()

send @ jquery.js:4

ajax @ jquery.js:4

(anonymous) @ ajax-pagination.js:4

dispatch @ jquery.js:3

r.handle @ jquery.js:3

Do you guys have any idea why?