Why can I sync on my PC? Not on Android phones

I installed the program on my PC and synchronized it in WebDAV mode. Everything is perfect.But definitely not working on Android. The app gives me “Network request failed” message. I tried all kinds of ways. It still nothing works.The version is the lastest.

Where did I set it up wrong? How can we solve this problem?

Plain http is not supported on Android, and non-standard ports may be a problem too.

Thank you. When I changed it to HTTPS, it works.