I am in the process of testing my form and have sent a link to colleagues to test who are in a different country than me. Colleagues who are in the same country do not have this issue - we can all submit. Could it be an issue in the settings column?
Welcome to the ODK forum, @amzie91! We're glad you're here. When you get a chance, please introduce yourself on this forum thread. I'd also encourage you to add a picture as your avatar because it helps build community!
For your question about the link...
Just to confirm, this is using an ODK Central server that you have set up?
Are you able to share the country of the server, and the country where the users are having the issue?
For the "Unknown submission problem on data server." error...
Did you update the draft after providing them with access?
For the QR code...
The QR code for a draft is used to configure ODK Collect on a mobile device and must be scanned from within the Collect app which is Android only. Please read to the end of this section of the docs: https://docs.getodk.org/central-forms/#working-with-form-drafts