WordPress: Plugin: LayerSider: admin-ajax.php: Error 403
Colleagues went to update the Top Banners of the Official website.
Got an error, however:
domain.hk says
It seems there is a server issue that prevented LayerSlider from saving your work. Please check LayerSlider → Options → System Status for potential errors, try to temporary disable themes/plugins to rule out incompatibility issues or contact your hosting provider to resolve server configuration problems. Your HTTP server thrown the following error:
The website runs the Plugin - LayerSlider to set the Banners.
At the beginning, set the WordPress's Logs. Did not find any related information.
Finally, identified the question that was from the Web Application Firewall (WAF) - ModSecurity.
WAF blocked it.
Error: [client A.B.C.D] ModSecurity: ... [severity "CRITICAL"] Access denied with code 403 (phase 2). Match of "beginsWith %{request_headers.host}" against "TX:1" required. [hostname "domain.hk"] [uri "/wp-admin/admin-ajax.php"] [unique_id "Yblc02uTbIKVNYxZxpFbBQAAAUw"], referer: https://domain.hk/wp-admin/admin.php?page=layerslider&action=edit&id=2
For colleagues, temporarily changed it to only monitor the website.
After it was the update done, set it back to on.
Update