I\'m having trouble getting universal links to work
The Apple validator checks some other things that are not necessary for Universal Links to work, and unfortunately that often results on false positive error messages. The file at https://couchsurfing.com/apple-app-site-association looks good to me, and it passes this validator just fine.
When clicking on a valid link, does the app not open, or just the delegate methods don't fire? These are two very different issues and would have different solutions. There are some troubleshooting steps you could try here, though some of those are specific to the Branch.io (full disclosure: I'm on the Branch team) linking platform.