Is this a security need, or a tracking need?
If it's really about TRACKING the sources, then I would say add Referer to the Embedded data in the survey flow, so that you can see which URL they came from.
If you need to also RESTRICT ACCESS to the survey on that basis, in that case, you would turn off the restriction in the survey settings (because that only allows one referer), and use the survey flow to manage it, eg adding branching under the Referer step, so that if Referer ( does not equal ) any of the expected referral sources, the survey terminates unsaved. << That would need some testing to make sure you have the exact Referer information that is expected and that there are no variations that might be introduced, but it would work around the single-referer limitation in the survey settings.

https://community.qualtrics.com/XMcommunity/discussion/comment/42657#Comment_42657Hi CarolK could you provide more information about how you do this to restrict access to the survey based on referral URL? The referral URL function in the screenshot by MikeB is not working at all for me...I would like to try using your method.

Hi sarasuzuki here is an example (in this case, I just used a fake URL as the referer, but the premise is the same... add the Referer variable to the survey, branch based on the Referer (exactly or "contains"). In my case, I only have two conditions, "came from the referrer" (sees questions) or "did not come from the referrer URL" (ends without saving based on the customized End step).
In your use case, you would probably want to confirm EXACTLY what the referer URL(s) will be and match based on matching or containing the full referrer URL. You could also use the referrer information in other places in the survey flow or for display logic, if it applies, once you have it in the survey flow.
I hope that helps!

https://community.qualtrics.com/XMcommunity/discussion/comment/43909#Comment_43909Thank you so much CarolK!!! This worked perfectly except I had to make sure to add the Embedded Data Field of Referer on the right hand side.
But thank you so much this solved a huge problem for me.