Rotate picture-preview on mobilephone

Hello, I have a small app that starts the camera on the mobile phone and allows shooting of pictures.

Unfortunately, the "preview" is shown rotated. The rotation has the value 270, although I did not change it.
I can turn the phone and apply what I want, the preview is always displayed "wrong". So either turned upside down, or turned 270 °.

I was looking for ways to fix that, but unfortunately I did not find it.

Has anyone solved this problem and would be willing to tell the solution here?

Thanks and regards!
Peter