The Test Connection feature is specifically testing what your MainWP Dashboard can “see” and what your MainWP Dashboard “sees” and what my MainWP Dashboard “sees” or what your browser “sees” can be completely different things.
To be sure that your Child Site can be connected to your MainWP Dashboard, first, you need to make sure that your MainWP Dashboard can communicate with the Child Site.
To verify that a Child Site can be connected to your MainWP Dashboard:
The result of the test will appear after a few seconds at the top of the page. In case you get a different result than
Connection test successful! (URL: yoururl.com (IP: xxx.xxx.xxx.xxx) - Received HTTP-code: 200 (OK))
there is a possibility that your child site won’t be able to connect to your MainWP Dashboard.
To find out more about what your HTTP Status Code means, please check the full list of HTTP Status Codes.