"Project key is not set" when Syncing Issues via Local Connection

Problem

Starting sync from the issue view responds with the following error message:

Incoming sync: first sync error
Project key is not set. You need to set a project key in the Sync Rules for {0} connection.

Cause

The problem occurs when starting sync for an issue that does not belong to one of the projects specified in the local Connection Sync Rules.

For example, when you create a local connection between project A and project B and then try to sync an issue from project C. In this case, the sync will be unsuccessful and the mentioned error will occur.

Solution

Every issue includes a Sync panel on the issue view. Please, make sure to select the correct Connection when starting sync from the issue view.