file upload problem, server not verified. tomcat

Hello. I am doing tests on my mobile with the apk of the application. The app loads some sounds that are in dropbox, with a direct link. It works fine, but sometimes, the message that appears in the photo comes out. When I give it to accept, the files have not been loaded correctly...

The translation of the text is:

"The server the application is connecting to is not verified.
Server: dl. dropboxusercontent.com"

"Issued for
common name:
tomcat
...

...

...
etc..."

"trust this server and make the connection?"

Thank you very much for the help.