Ah ok - so nothing to do with 180 degrees then. Is it maybe tilted slightly, like 7 to 15 degrees rather than 180 degrees? Might be something to do with this:
https://www.lmscope.com/en/Stereomikroskope_in_der_Fotodokumendation_en.htmlThough I would think each eye would see it tilt in the opposite direction? Is this what you get, or are both eyepiece views tilted the same way?
Do you get the same effect when you are not using a barlow lens? I don't have any barlow lenses for my stereo microscope, and when I look at flat horizontal things at any zoom range they look pretty flat and undistorted to me and in focus across the whole view for both eyes (though the view for each eye is slightly different as it is stereo). I am using 10X eyepieces and have 0.7x - 4.5x zoom control (for 7x to 45x magnification).
When I look at the objective lens area of my microscope (bottom of the microscope head) I see two small lenses at slightly different angles so I expect it is using Greenough principle (from the link above).
Perhaps the control to change between eyepiece view and camera view (that I mentioned in the previous post) is not fully clicked into place so the image for one eyepiece view shows as tilted?
I suggest you go through both manuals and also the other URLs I suggested and check that your microscope is properly set up. It could also be worth doing further research on general stereo microscope set up to make sure you have set it up correctly. There are lots of free resources available online for this.
If you are still having issues after this, then perhaps your microscope optics are not aligned properly and needs servicing, or replacement of the microscope.