Hi @Glenn Maxwell ,
You could also use site path in the Graph Api, the endpoint would be like the below:
https://graph.microsoft.com/v1.0/sites/{hostname}:/{relative-path}:/permissions
For example, you site url is https://contoso.sharepoint.com/sites/test, you could make a call to
POST https://graph.microsoft.com/v1.0/sites/contoso.sharepoint.com:/sites/test:/permissions
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