Why do we see POE error on the SonicWall TZ280P when 2 APs are connected with AT power

You get POE error on the SonicWall TZ280P

A TZ 280P connected to 2 Access Points: 

X6: Connects to SonicWave 224w and gets AT power

X7: Connects to SonicWave 231c and gets AF power

Now when we try changing the X7 from AF power to AT power we get the below error:

Is this Normal ?

Yes its a behavior on TZ80 devices.

Now question may arise, Does the TZ280P have enough budget to power up 2 AT devices - YES. 
Up to 4x AT devices are supported: 
https://sonicwall.atlassian.net/wiki/spaces/GEN8/pages/71793565/GEN8+POE+Functional+Specification

But the error indicated below suggests that TZ280P thinks that SonicPoint attached to port X7 doesn't negotiate AT, so it negotiates the common denominator: AF.

Gen8 supports up to 4 AT devices.

TZ 280P is correctly using AF power for SonicWave 231C. On GEN6 also the SonicWave 231C is using the AF power.  

The only difference is that on GEN6 it does not show a Pop-Up error if we set the port to AT, it automatically changes back to AF.