Hi @Mark Smith
Try:
https://graph.microsoft.com/v1.0/me?$expand=manager($levels=max;$select=id,displayName)&$select=id,displayName&$count=true
Cited from:
Example 2: Get manager chain up to the root level
If this doesn't work can you please provide what you are seeing and what tools you are using to send this GET request to?
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If this is helpful please accept answer.