The video below will guide you through the process of creating a PowerApp Custom Connector to the Microsoft Booking API via Microsoft Graph API.
I follow a 3-step process by first setting up a new Azure App Registration to handle the authentication and authorization to use Graph API. Next, we setup a new Postman collection that will contain the authorization and any queries or request that you want in your connector. And lastly, we export the Postman collection and that is then used to import into a new Custom Connector in PowerApps.
The following settings are referenced throughout the video.