Form Builder form creating duplicate contact when logging activity (volunteer hours)

Question

I created a Form Builder form, with "accessible on front-end of website" ticked, "generic: allow all users" permission set; "contact source" = "log volunteer hours" on Individual 1; and "added by" = "Individual 1", "activity type" = "Volunteer", and "activity status" = "completed" on Activity 1. The security for both Individual 1 and Activity 1 is "form-based", and "allowed actions" include both create and update.

I'd like to use this form to submit a volunteer's hours (duration) as activity against existing contact. Right now, the form creates a new contact with the entered activity information every time it's submitted, but this isn't the right behaviour as it creates duplicate contacts (a different one for each activity logged). Have I got some of the Form Builder form parameters incorrect, which is causing this behaviour?

Answer 1

I have a partial solution. If I add an "Existing Contact" field to the top of the form and the constituent selects their name using this additional control, then when the form is submitted it doesn't create a duplicate contact but rather the activity (e.g., "visit nursing home" for [duration] "2" [hours]) is appended to the list of activities for the constituent in question. The remaining issue is that any constituent can now use this control to look up other members in the database. Ideally, I'd like the control to only show contacts within a certain group, e.g., "Volunteers". Then I could password protect the WordPress page with this control allowing only volunteers to access it.