I am using Enterprise with a federated service. Survey has been deployed using an existing Feature Service using the submission URL. Feature service allows Update only.
I used these steps to set things up;
Create Survey123 form and publish to Portal (as hosted service)
Download Form (table) to File GDB
Copy table from File GDB to SDE database
Create relationship class between existing Feature Class and new table
Publish feature class and table as Feature Service
Open Survey123 Connect, New Survey>From Feature Service
Add formatting back to Survey123 form
Ensure submission url is valid and form name correct
Re-Publish