Summary

When creating tickets via the JIRA Service Desk API, it's not possible to add other customers as Request Participants using their email address.

Steps to Reproduce

1. Create a Service Desk ticket via API, adding a request participant using their email address as the parameter:

   curl  -X POST --user 'user:pass' -H 'content-type: application/json' 'https://site.atlassian.net/rest/servicedeskapi/request' -d '{
   "serviceDeskId": "<id>",
   "requestTypeId": "<id>",
   "requestFieldValues":
   
   { "summary": "Creating a Test Issue", "description": "Lorem ipsum" }
   ,
   "requestParticipants": [
   "email@domain.com"]
   }'

Expected Results

The ticket is created and "email@domain.com" is added as a participant.

Actual Results

The following error is returned:

{"errorMessage":"Sorry, but the following usernames could not be added as participant to this request: email@domain.com","i18nErrorMessage":{"i18nKey":"sd.request.participants.username.error","parameters":["email@domain.com"]}}

Notes/Workaround

It is possible to add request participants using their username instead. However, with the recent changes to usernames, there's no easy way to find customer's usernames.

Service Desk Agents can retrieve this through the Experimental API (/rest/servicedeskapi/servicedesk/<service_desk_id>/customer)