Thank you for your post.
The issue sounds like it is a file format issue, but I’m not sure without seeing it. Or, you may be importing in the wrong area causing it to think it’s the wrong file format. For example, you could be importing in the map section and that area will only accept Map type formats.
Additionally, if you could send an email to our support team: email@example.com and attach the file you are trying to import; they will be able to assist you and possibly replicate the issue you are experiencing.
When importing map features (points, lines, etc.) to the Avenza Maps app you have to import in the Layers tab or within the map itself. Here is an article on our support website that may help you: https://support.avenzamaps.com/hc/en-us/articles/360035074752-Importing-map-features-to-a-map