Profile Manager cannot download

Is the lastest macOS Server 5.7.1 's remote management cannot connect the new device of MDM which is using IOS12 or above?

My ipad already connected to the MDM system and use it smoothly. Because of the wifi connection have some problem that I need to format it.

When I format the ipad and start to connect to the server, it can find the server, but it cannot download the Profile and notice the following error:

「Profile Installation failed. A network error occured.」

I read this error before I update the macOS Server. The solution is downgrade the ipad to IOS 11.4.1 and it can download the profile. But I cannot downgrade to IOS 11 because the gate is closed:(

Does anyone have a solution to this problem? Thank you all.