Problem

Error Detail message
javax.scripts.ScriptException: com.exalate.api,exception.IssueTrackerException: Project key is invalid.
Please check your create processor script.

Cause

Jira requires a project to be selected for creating issues. When you received incoming sync form the remote side you should specify the project they'll be created in.

This error is usually caused by the project key not set or not valid in the Create Processor.

Solution

Set the project key in the Create processor.

You can do that under Connections - edit the Connection - Sync Rules tab.