Create Event to existing contact from Calendly booking

Create Event to existing contact from Calendly booking

I I want my calendly bookings transfered to Zoho CRM with the following steps:
1. Appointment is booked
2. Is there an existing contact? If YES, then create event (with booking data). If NO, then to step 3
3. Is there an existing lead? If YES, then create event (with booking data). If NO, then to step 4
4. Create lead. Create event to that lead with booking data.

Steps 3 and 4 work fine, but step 2 doesnt work.
I get the error: "Zoho CRM says "Zoho CRM says 'invalid data'. Check the input for $se_module and try again."

I set up the step like this:
related module: contacts
related to: ${fetchContact_1.id} from the get contact step before.

Why cant an event be created to a contact? Setting the relation to the contact doesnt word. The same ways works with leads, though.