Fotografos

Correct. It seems the process of checking the firmware allowed communication between the camera and lens. You should probably then update the firmware if needed. In my case the lens firmware was the latest but the camera was one minor update behind. Again as I mentioned there may be other reasons for the error message, but it's worth a try.

Although there may be multiple reasons for the error message "TURN CAMERA ON AND OFF AGAIN" including a true mechanical problem, I may have another solution that might work for some. I recently purchased a new 10-24 XF zoom. Upon initial installation on both a X-T3 and an X-T30 body that I own, I immediatelly got the dreaded message. I swapped bodies, turned on/off multiple times took out the battery for 2 minutes and reinstalled it, cleaned the contacts multiple times, all to no avail. Finally I thought of checking the Body and lens firmware (in the off position press and hold the Disp/Back button and turn on the camera) and "Voila" the problem was solved. No more "TURN CAMERA ON AND OFF AGAIN" on either body and several attempts of mounting and dismounting the lens were immediately successful. Hopefully I will not see it again.