What does a 403 error with "The app is not installed on this instance" mean?

Confluence Development Confluence Cloud
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1

I’m facing the same issue as reported here.

I’m trying to fetch Confluence spaces (https://api.atlassian.com/ex/confluence/${MY_CLOUD_ID}/api/v2/spaces) sending a valid Bearer token, but I’m getting the following error:

{"code":403,"message":"The app is not installed on this instance"}

I’m using the refresh token to get a new valid token.