On my community I have a page with a flow component that shows a screen flow with form fields.

For one of the fields need to be prefilled with a string via the URL. This field is populated via a variable in the flow called ReferralCode.

Passing a value in the variable via the internal url works fine. When I try to do the same for the community URL it does not pass the value of the url.

I tried the following url:
https://test-shbl.cs101.force.com/shbl/s/registration?ReferralCode=XYZ1

Is this even possible and if yes how can I achieve this?