Error uploading gpx files

In the past few days, I always get the following error when I try to import a new gpx file in my repository (using Firefox v. 95.0.2): "Secure connection failed".

If I push on the "Retry" button, it doesn't work. I also tried other files (also generated by Cycle Travel itself), but I get the same error.

No chances to "accept" the unsecure connection and move forward with the import.

If I click on "More Information" button, Firefox just returns its standard generic security messages, so it is not clear the specific reason of the error.

Can you help? Any ideas how to solve?

MN_Scorzarolo_Sabbioneta_Campitello_MN

Percorso da Mantova a Sabbioneta, passando dall'argeine del Po (Scorzarolo), con ritorno da Campitello e Grazie