How to make a FormBuilder form that creates (1) Case (2) an Activity attached to that case, when completed by an anonymous user?

Question

This is the desired behaviour:

1. anonymous user completes volunteer application form
2. the form creates:
   • a new contact record for the user
   • a new case of type Volunteering for that user
   • an activity, say 'Volunteer Form Submitted', on that case

I've been able to create a case and a separate activity, but not an activity that belongs to the case.

NB this has to work for anonymous users.

Possibly connected - what is this setting for (below)?

Edit: screenshot showing issue with Cases tab in contact summary:

Answer 1

The 'File on Case' setting in Form Builder is used to assign an Activity to a Case (where these are both created by the form), for e.g. in Activity 1 tab you set File on Case = Case 1.

However, for this to work properly when the form is completed by an anonymous user, you must set Case Creator = Individual 1 (if Individual 1 is the anonymous user completing the form).