Hi @Steibl Thomas Thanks for reaching out, This feature is still in Private Preview you will have an application registered with Azure AD. Email your application ID to mailto:ask-graph-and-grid@abdou .microsoft.com?subject=Please allow my Azure AD application with ID to send events through Graph API so that the Microsoft Graph API team can add your application ID to allow list to use this new capability.
Graph API team will provide you with Partner registration id with that you can add a partner authorization as shown below
let me know incase of further queries, I would be happy to assist you.