Can you please check if there is any output (errors) in the browser's console ?
What web server are you using ?
REST API relies on URL rewriting to use /mantis/api/rest/xxx URLs. Can you confirm that URL rewriting is configured correctly ?

I faced a similar issue in the past in a plugin (see https://github.com/mantisbt-plugins/Snippets/issues/31). Can you try modifiying js/adm_config_report.js, at line 45

-                   content.load('api/rest/internal/config_display',req_data);
+                   content.load('api/rest/index.php/internal/config_display',req_data);

Web server is Apache/2.4.7 (Ubuntu).
Module rewrite says Module rewrite already enabled.
When you click you get AJAX Post 404 in console (check image).

Your proposed modification resolves an issue.

image-2.png (19,491 bytes)   

image-2.png (19,491 bytes)   

@kuz30 thanks for the feedback.

I'll implement the proposed change in core as I think that internal REST API call need to work regardless of the webserver's configuration.

That being said, there is something wrong with your configuration. If you're planning to use the REST API externally, you'll need to sort this out otherwise the expected "nice" URLS like http://path.to/mantis/api/rest/<endpoint> will not work and you'll need to add the /index.php bit as per my earlier message

Note: the mod rewrite configuration is handled via an .htaccess file. Maybe your webserver config is blocking that.

PR https://github.com/mantisbt/mantisbt/pull/1559