How to fix "xmlhttprequest cannot load" error when installing opencart 2.3.0.0 module?

Question

opencart

When trying to install the module in opencart, the alert
"error undefined" is displayed

in the browser console, while outputting:
"XMLHttpRequest cannot load trendshopnew/admin/index.php?route=extension/insta... . No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin '<site name>' is therefore not allowed access."

Playable on OpenServer 5.2.2