I have the same problem… black key popped off. It is Xkey 37 (not air). I didn’t do anything unusual. The keyboard was just sitting and one day I went to use it and a black key was no longer attached to the keyboard. There is also a stiff wire dis-attached from the keyboard. Does not seem to have any broken parts. Just that the 10th black key from the left is popped off.
Please tell me how to pop the key back on.