To get feedback on your Proto.io project, go to Share (either in the Editor or in the Dashboard under Project->Manage Share links), create a new Share link (shared with everyone, not password protected), go to the ‘User Testing’ tab and copy the generated link to use in Validately.
Be sure that your link has /Validately/ at the end, or the link will appear to be broken in your test set up and direct the participant to download the Proto.io app.