@Jeroen H There are two separate things that you are mentioning here.
- Getting notifications to work. This has nothing to do with eventgrid. setting up event grid will not trigger "IncomingCallHandler". https://learn.microsoft.com/en-us/azure/communication-services/concepts/notifications#deliver-push-notifications-via-azure-notification-hubs Follow the steps under Deliver push notifications via Azure Notification Hubs from the above link to get push notifications working.
- Now events was mentioned above. this will not result in getting your "incomingCallHandler" invoked. But you can get all the incoming call events to a webhook on your service. You can follow - Quickstart - Subscribe to Azure Communication Services Events - An Azure Communication Services quickstart | Microsoft Learn
You need a service which exposes a webhook publicly and you can should configure it to eventgrid.
If you properly handle the validation event in the service, the event subscription should succeed on the portal.
- and 2) are orthogonal things. with events going to event grid to webhook to customer's service, they can potentially loop it back into their app if they have built their own push notification system. if not, please strictly follow 1) to getting push notifications working for the app. you can use 2) for auditing, tracking incoming calls and also if you want to answer the calls from a service/server app using our server sdk.