I can not access the link using iframe

I try to access the different URLs from my current domain using iframe but it's not loading into my domain but it's working in the localhost. I used this code X-Frame-Options ALLOW-FROM=http://my-secound-url.com in my .htaccess nothing happened and I used this code X-Frame-Options: ALLOW-FROM http://my-secound-url.com inside my httpd.conf file and I restart the server it's showing the error

Job for httpd.service failed because the control process exited with error code. See "systemctl status httpd.service" and "journalctl -xe" for details.

My Iframe code

<iframe style="height: 283px;width: 100%;" src="http://secound-url.com" scrolling="no"></iframe>

And I check my site through developer option console it's showing this message,

Mixed Content: The page at 'https://my-domain.com/' was loaded over HTTPS, but requested an insecure resource 'http://secound-url.com'. This request has been blocked; the content must be served over HTTPS.

I using the Amazon EC2 server and my domain is SSL active site. Please help me and give a solution to access the different URL inside my domain