Advanced iframe debug console - l: local messages, r: remote messages
User agent: CCBot/2.0 (https://commoncrawl.org/faq/)

Headers of http://www.gmatjakarta.com:
HTTP/1.1 301 Moved Permanently
Server: nginx
Date: Wed, 02 Dec 2020 15:39:40 GMT
Content-Type: text/html; charset=UTF-8
Connection: keep-alive
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
X-Cache-Enabled: True
X-Redirect-By: WordPress
Set-Cookie: PHPSESSID=0ce44c2c12bfaf3617508ccd9deae3a9; path=/
Location: http://gmatjakarta.com/
alt-svc: quic=":443"; ma=86400; v="43,39"
Host-Header: b7440e60b07ee7b8044761568fab26e8

HTTP/1.1 200 OK
Server: nginx
Date: Wed, 02 Dec 2020 15:39:40 GMT
Content-Type: text/html; charset=UTF-8
Connection: keep-alive
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
X-Cache-Enabled: True
Link: ; rel="https://api.w.org/", ; rel="alternate"; type="application/json", ; rel=shortlink
Set-Cookie: PHPSESSID=e4f9176892f4b472dea3df77e7b23b3b; path=/
alt-svc: quic=":443"; ma=86400; v="43,39"
Host-Header: b7440e60b07ee7b8044761568fab26e8

The url you try to include is HTTP and your page is HTTPS. This is not supported by most modern browsers. See this blog for details. The url is redirected to http://gmatjakarta.com/ (http status: 200)!

Http iframes are not shown in https pages in many major browsers. Please read this post for details.