Hi Mira,
FYI: if you've configured Portal for ArcGIS with a hosting server and the ArcGIS Data Store correctly, there are no additional parameters or settings that need to be set in the Portal sharing API to enable Survey123 to work.
Since you're using Survey123 Connect, try this to get more info on the issue.
1. Open Survey123 Connect.
2. In the lower left corner of the UI, click the gear icon to open the Survey123 Connect Settings dialog.
3. Click Diagnostics.
4. Click the Logging switch button to turn on logging. Ensure you know the location of the log file.
5. Click OK.
Now try and sign into your Portal for ArcGIS instance and after you get the error, navigate to the log location and view the log file. There may be some useful information there.
But as I've said, I suspect something is NOT configured correctly with your Portal for ArcGIS with hosting server and the ArcGIS Data Store. If you can't see any useful information in the log file, please contact Esri Tech Support and they can help you investigate further.
Hope this helps,