@FreddyD Thanks for posting in our Q&A.
For this issue, please check if you choose one of the permissions in the following link:
Because I didn't have an iOS device (supervised only), I can't repeat this test. However, I can share you the steps to get the correct request.
1.Enter "F12" to open the DevTools.
2.Click on the "Lost mode" in intune portal and we can see many requests under Network in DevTools.
3.Find the target graph api name and the Request Method shows "post" in DevTools. Then we will get the correct Request URL.
4.Click on Payload > View Source and we will see the correct request body.
5.Cope the Request URL in step3 and the Request Body in step4 in Graph and check if it works.
Hope it will give you some ideas.
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