Unable to import from exported repo

I’m running gitlab-ce 16.2.2 and am unable to import repos. To simplify the problem I have
created a project on the server using a template, exported it and then tried to import it to
a new project. I get “You need to upload a GitLab project export archive (ending in .gz).”
although the file I have selected is a .tar.gz file and is a valid tar file What am I doing wrong ?

Thanks and Best Wishes