WP_Error Object ( [errors] => Array ( [http_request_failed] => Array (  => cURL error 28: Operation timed out after 45001 milliseconds with 534 out of 833 bytes received ) ) [error_data] => Array ( ) ) – ERROR
I was using a self-managed VPS so could not ask for support from the hosting company thus I keep searching online about this issue. I also sent email to plugin developer, but could not get a reply in last 48 hours from now.
I installed the plugin TLS 1.2 Compatibility Test, although it is not updated for more than 3 years but it works on my latest version of WordPress till today. It shows that the version of my CURL library is not latest, so I followed this tutorial to update my CURL to latest version and this solved the issue.