Eventbrite to Salesforce - error message

hello!

Trying to push eventbrite attendee registration into Salesforce. We capture this in a custom “participant” object.  A very simple object with only three look up fields which ultimately creates a list of attendees on a related Case/Service object which captures the event itself. 1 event, many participants.

Participant record and related service record screen shot below. As you can see-  the Service number is the field that ties these two objects together.

Zap currently set up to 

1. Trigger- new attendee registers in eventbrite
2. Action- find records in salesforce-  
   1. Action successfully finds correct event record in salesforce related to attendee registration - no error.

…but when I try to link a participant record to that event, I get an error…

1. Action - create record in salesforce-
   1. I linked the service/case number field through step 2. It shows up with correct service number in the preview- populated from testing step 2.
   2. But then I get the error screen shot at the bottom when zap is tested.

Thank you for any help!