Unable to view images in project wiki

I’m running gitlab community edition 16.5.1 and am unable to see images in a project wiki.
I can see the wiki, after I attach an image and click on the link I get a new broswer tab with the error
the image … cannot be displayed as it contains errors

I can view the image outside gitlab, the apache gitlab logs give a 404 error.
Is the problem that the image contains an error or the generated link is incorrect or the
image has not been downloaded. How can I find out

Thank you