How to access secure data for report

Our organisation has a Survey123 form that is submitted by people outside of the organisation. So the data is submitted anonymously to our ArcGIS enterprise server. After the survey is submitted we want to generate a report with VSR and send that report to our administration and the person who submitted it. The data is collected in a feature service that is not public available. I created a workflow that is triggered by a webhook and that runs the run report activity. So far so good. Unfortunately the generation of the report fails because VSR can't access the data. I added a webtier user and password to the Data Source (Our ArcGIS enterprise server), but this doesn't seem to help.

I know I could add the data through a JSON data source, but that way I'm unable to use the geometry to generate a map in the report.

Does anyone knows a way to get the data without exposing the feature service to the public?