Server 10.3.1 not federated.
I followed the above documentation to get a survey123 repeat working to no avail. I tried every combination of globalID, GUID, parent--child relationship in the feat. service relationship class to no avail.
After publishing the feat. service, I added the REST feat. service endpoint URL as an item to AGOL, saved the credentials with the item, then included that arcgis.utility....URL in the xlsform service_url field. The name of the repeat was exactly the same as the related table name in the feat. service.
Using survey123 connect, every time I tried to publish the survey to AGOL, I would get the error, "parent relationship <relationship name from child to parent> not found from <related table name>".
If I re-publish the feat. service w/out the relationship class, then re-publish the survey w/out the repeat, everything worked great, and we are able to host the survey123 feat. service on our non-federated server. Which is ideal for us since we are running low on AGOL credits.
Another issue: I can publish a survey123 repeat to AGOL, the hosted feat. service is automatically created in AGOL and everything works as expected. HOWEVER, if you try to download the hosted feat. service as a FGDB it fails because it contains a relationship, i.e. related table. If you download as .csv everything works as expected.
Looks like a few more relationship bugs exist.