I have two iPhone 11s and one iPad Pro. I tried to connect with MotionLive with Live Face, and I also tried "telnet xx.xx.xxx 999" from a PC. The following three cases are the results.
A: iPhone 11 with 15.1, iClone connects fine, telnet is fine.
B: iPhone 11 with 15.2, iClone fails to connect, telnet is failed.
C: iPad Pro with 15.1, iClone connects fine, telnet is fine.

Another thing I notice is that in 15.2, the Live Face does not acquire the wifi network nor the cellular network connection.

So, could anyone please verify that or update the Live Face App? Thanks.

I only connect via ethernet, and it works fine with 15.2 (although I will say that I now no longer have to put the phone in airplane mode, so they fixed something in the newest release.  Thanks!).

Since it does work fine via ethernet I'm kinda guessing it's not an iOS issue but perhaps folks who do connect via wi-fi can see what their experiences are (I've never been particularly successful using wi-fi since I first got Live Face a few years ago).

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Alienware Aurora R16, Win 11, i9-149000KF, 3.20GHz CPU, 64GB RAM, RTX 4090 (24GB), Samsung 870 Pro 8TB, Gen3 MVNe M-2 SSD, 4TBx2, 39" Alienware Widescreen Monitor
Mike "ex-genius" Kelley

Tried iPhone 13 Pro iOS 15.3 and is working OK by WiFi.

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Software developer. iClone hobbyist since January 11, 2020. Best work so far: Robots among us: The Lab and The sad end of a legend
In progress: Black Mamba
AMD Ryzen 3950X 16C/32T 4.2 GHz, 64GB RAM, RTX2080 11GB, 2TB Samsung 970 Pro SSD, 8TB Seagate BarraCuda HDD, Win11 64-bit, iClone 8.12

iOS 15.3? Beta? It has not been released yet.

Yes, I'm on beta (today they just released public beta 2) Unfortunately, I no longer have 15.2 on any of my devices to try, but I don't think the issue is due to the OS version, I rather assuming is a problem of subnet on your WiFi configuration. Try the following: on your iPhone, check in the current WiFi "i" its local IP address. Assume is aaa.bbb.ccc.xxx. Then check your computer running iClone its local IP address (on the WiFi icon next to clock, click the WiFi icon, look which WiFi is "connected", then click properties to seee the local IP). In order the communication to work properly, its IP should be aaa.bbb.ccc.yyy. If the first three groups are not identical, then (generally, but it depends of a particular configuraton) iPhone's LiveFace would not be able to discover the iClone. Hope it helps.

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Software developer. iClone hobbyist since January 11, 2020. Best work so far: Robots among us: The Lab and The sad end of a legend
In progress: Black Mamba
AMD Ryzen 3950X 16C/32T 4.2 GHz, 64GB RAM, RTX2080 11GB, 2TB Samsung 970 Pro SSD, 8TB Seagate BarraCuda HDD, Win11 64-bit, iClone 8.12

Thank you all for your inputs.
After I update my iPad to 15.2.1, and it connects to iClone, I realize that it is not an iOS problem but a network problem. After I dig a little bit, I think I might locate the problem.
In China, there is a specific setup called "Apps using WLAN & cellular". This setting is confirmed by Apple @ Link 1, Link 2. Fig 1 and Fig 2 show the different settings. Fig 1 is the setting that can connect to iClone. Fig 2 is the setting that can not connect to iClone.
The first time you launch an app, it will ask you your network preference, as shown in the following YouTube App settings (Fig 3). Wireless Data setting is set to WLAN & Cellular. The Live Face App does not have such a setting (Fig 4).  According to Fig 4, Live Face only has the camera and Siri access, and it will not have local network access.

According to a stackoverflow solution, the Motion Live team might need to add some code to the Live and recompile it. The code needed is in the stackoverflow link.

In the meantime (and, perhaps, forever - I would NOT hold my breath on that app ever being changed) you can connect via ethernet (it's more reliable and faster anyway).

Just buy a $30 ethernet adapter and you're good to go.

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Alienware Aurora R16, Win 11, i9-149000KF, 3.20GHz CPU, 64GB RAM, RTX 4090 (24GB), Samsung 870 Pro 8TB, Gen3 MVNe M-2 SSD, 4TBx2, 39" Alienware Widescreen Monitor
Mike "ex-genius" Kelley

@beijing
using iphone 12 pro 
IOS 15.2
live link failed
also telnet 999 cannot connect