Is there any way in Survey 123 Connect to pull call a webhook while filling out a form? Then return the data back into the from to auto populate fields?
If you are not planning on sharing your survey publicly you can use a custom JavaScript function to send a request to any API you like and work with the data from the response in your survey. Please see this Esri Community blog and this documentation for more information. We also have a JavaScript sample available in Survey123 Connect that shows how to work with third party API's.
