Hi Ryan,
The error code you see is very generic. Has this form successfully sent survey information before, on this or another device? The wifi network the iPad is connected to is on the same network as the Portal?
A couple of things to test:
1) Can you open the Portal's home page in a browser on the iPad? From there, can you get to the item details page for the survey's feature service and access it's Service Url? (testing the network connection of the iPad)
2) Can you add points to your survey's feature class via the Portal's map viewer? (testing the operation of the feature service)
It would also be helpful of you could capture a log while attempting to submit data. See instructions at Troubleshoot—Survey123 for ArcGIS | ArcGIS (do not wait for a console to appear, just click on the switch to start logging). After the submission attempt, the log file can be extracted by:
1) Connect the iPad to a computer with iTunes
2) Open iTunes, once available, click on the iPad button to go to it's configuration
3) In the left side pane, click on 'Apps'
4) in the main window, scroll down past the first list of apps to the second list, which is to show files that can be transferred back & forth.
5) Select Survey123 on the list, and then select the 'ArcGIS' folder
6) At the bottom of the file transfer list is a 'Save to...' button to copy out the data from the iPad.
7) The log file will be in the 'ArcGIS\AppStudio\Logs' directory.