JIRA Application Development panel displays error - Couldn't read data
Within the JIRA Application, the Development panel displays a "Couldn't read data from (application name)" message, even though the Atlassian application involved (for example, Bitbucket Server, Bamboo, Fisheye or Crucible) is of the correct version.
Consequently, information from the other application cannot be displayed in the Development Panel.
Screenshot: Typical error message in the Development panel, when JIRA is connected to a Stash instance
Two-legged authentication (2LO) is not enabled for the application link between the JIRA application and the other Atlassian application (Stash, Bitbucket, Bamboo, Fisheye or Crucible).
On Atlassian Cloud "2 Legged OAuth with Impersonation" is not available. "2 Legged OAuth, without impersonation", is required for the Development Panel.
For an existing application link between the JIRA application and another Atlassian application (Stash, Bamboo, Fisheye or Crucible), the administrator must enable 2-legged authentication for both outgoing and incoming authentication in both applications to see information from that application in the Development Panel. That can all be done from either the JIRA end or from the other application.
You can follow the guide at How to adjust an existing Application Link to use OAuth to do this, making sure to allow 2-legged oauth on both sides of the application link.
Read more about configuring OAuth authentication, including security implications, at Configuring authentication for an application link.