Can't connect to self signed certificate https server using Android app


I deploy a rocketchat server on my vps server.

I created a self signed certificate with Custom Root CA and configured it in nginx config file.

And I configured a SSL Reverse Proxy using nginx.

Because I don’t own a domain name,I use IP address to visit rocketchat server.For example,https://

Now I can visit rocket server successful with web browser and desktop app.
I can’t connect to server with android app using https.(https://
Error message is “An error has occurred while checking your server version,please try again.”
But I can connect while using http.(http://

Android apk is downloaded from github release.And I installed version3.3.0.

Rocketchat server version is 0.74.3.
Android version is 8.0.0.

Can you please help me to resolve this problem?