Permissions inconsistency between rest/api and rest/servicedeskapi

Hi! I am a developer troubleshooting an integration with Jira. We have used OAuth to connect to Jira, and are successfully calling{org-id}/rest/servicedeskapi/...

But, when I make a call to{org-id}/rest/api/latest/search/{jql}, I am getting a 403 error with the error message {"errorMessages":["The app is not installed on this instance."]}. I can successfully make this call to other org-ids, so I know that my jql is correct. The user who I am OAuthed as is a Jira Admin. I also confirmed that Jira Service Management is active.

What other configuration or permission issues could cause this error?