If you would like to track Segment users across multiple domains e.g:
Site 1: https://www.example.com
Site 2: https://www.flow.example.com (the domain hosting the Formsort flow)
You must explicitly set and pass the responder UUID from the top level domain to the one hosting the Formsort flow. This can be done for both with a direct link deployment or an embedded flow.
Setup
Step 1: Add the responder_user_id as an external variable
Navigate to the variable tab inside of a flow and add an external variable.
Name the variable "responder_id" and set the data classification toggle to responder_user_id. This variable will be used to pass the responder id as a query parameter from https://www.example.com to https://www.flow.example.com
Step 2: Set external user id as identifier in Segment integration settings
In Formsort's Segment integration settings, toggle on "Use user_id from answers to identify" option
Step 3: Pass the responder id as a query parameter to responders hitting the flow
Passing via direct link
After deploying the flow with the variable set in Step 1, you can now pass a Segment user id into the flow as a query parameter.