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Hi, this usually means the embedded app user is not matching the Copilot Studio access settings.
Check that the bot is published, the security settings allow your user or group, and you are signing in with the same Entra ID tenant used by the copilot. Also confirm the embedded app is using the correct bot/environment endpoint.
Even as owner, the embedded channel can still block access if the auth token, tenant, or published bot version does not match.