Can not calibrate Images captured with EKOS (stellarmate) in Pixinsight? #34349
I think the fits warning is normal. Pixinsight tries to push you to use the xisf file format over fits for the reason described in the error you got.
If you are trying to calibrate with Cal frames captured with a different tool than ekos the incompatible geometry error can happen. This has to do with how different drivers read out the camera. Try grabbing some Cal frames within ekos.
Regarding the geometry error - frames pulled via indi w/ Ekos and other clients (PixInsight included) are definitely different than those captured with TheSkyX on Linux (incl RPi) for at least the FLI drivers. As an example I get overscan margins w/ indi but not with TSX. It's probable that other cameras are similar. I wouldn't be surprised if this is the case.
PixInsight will error if the image geometry (matrix size, possibly pixel depth too) is not exactly the same between the calibrating frame and the frame to be calibrated - they can't line up.