Azure Communication Services - event subscription not created for Powerautomate trigger

Question

Scenario that works:

1. I have set up Azure email communication Service with my VS Subscription.
2. Emails can be sent with C# client program and are received.
3. A Powerautomate flow with trigger "When a resource event occurs" is working fine. This trigger automatically creates an event subscription in Azure for my communication service resource.

Scenario what does NOT work

1. An Admin created the communication Service with a corparate subscription
2. Emails can be sent with C# client program and are received.
3. A Powerautomate flow with trigger "When a resource event occurs" did not create the event subscription in Azure for the communication service resource. The error message (see below) in the flow looks like I miss some permissions, but what kind of permission is required? The client '******@yyy.COM' with object id '<...removed....>' does not have authorization to perform action 'Microsoft.EventGrid/eventSubscriptions/write' over scope '/subscriptions/<....removed....>/providers/Microsoft.Communication/CommunicationServices/<....removed....>-communication-svc-prd/providers/Microsoft.EventGrid/eventSubscriptions/LogicApp1f92be5a-<....removed....>' or the scope is invalid. If access was recently granted, please refresh your credentials.