Question Character in correct pose, but "Not in T pose" error still appears

Hi, I'm working with an humanoid character, and when trying to configure its avatar, I found that the fingertips are twisted. If I try to correct them, by resetting to Bind Pose or manually, the "Character not in T Pose" error pops up. If I try to Enforce T Pose, the error goes away, but the pose is incorrect.
I have checked the model in Blender, and the skeleton is correct.
What could be causing this issue? How the T Pose detection works?

 

If I recall correctly it checks that every bone in the arms is 90 degrees relatively to the spine, if it is even a tiny bit off it will complain and if you force it it will try to make it 90 degrees.