@Apmucm 

For all need guideline for successful setup with P9 model. Try following in deco 

1. In MORE menu, go to Advanced. In LAN IP menu, change ip adddress to 192.168.1.1 and Subnet Mask remain 255.255.255.0. Save the setting.

2. Make sure Fast Roaming is disabled.

3. In MORE menu, go to Wifi Setting. Turned on the guess network with 2.4ghz wifi only.

4. with your mobile device connect to guess network. Start Xiaomi Cam setup.

I got the same problem with my Deco M5. My sister house using M5 and Xiaomi Mi home 360 camera surveillance and its ran great. Then I bring the camera back to my house and it cannot connect to my M5 mesh (M5 firmware is up to date).

IPTV is very good feature for M5, but cannot connect to camera surveillance is not a great thing.

@Viet.Pham  simple & only way: turn off Fast Roaming. it'll work as expect

@Apmucm hi there, i also have the same problem which my xiaomi cctv can not be connected via deco m4. But using old router , there was no issue. 

Finally i have found the solution to my problem by let the QR code to be appeared on my smart tv (big screen) and scanned the camera by facing it to the TV. It worked. 

You may screen shot the QR code and let it mirror to the smart tv. Then scanned the xiaomi cctv by facing to the smart tv.

Hope it will also work for whom has the same problem. 

Cheers..