this one helps. This seems to be a question of reading the API documentation carefully. Assuming you are trying to call an orchestrator as described here, I find this example that looks a lot like yours.
This might help you I have an Azure AD Application where I need to add an extra appRole in the appRoles section within the service principal with Powershell. I use an Invoke-RestMethod to the Graph API with the following API Url: https://graph.microsoft.com/beta/servicePrincipals/AppID