but seems the format incompatible with the webhook notification from meraki, then perhaps with an api gateway in the middle converting the format from meraki to the microsoft format you can do something.
That's correct, as the Meraki webhook format contains data from the Meraki dashboard including information about the organization, network, device, and specific alert. The alert is not just a chat message, which is why you cannot natively ingest it into any messaging application (Webex Teams, Microsoft Teams, Slack, etc.), and will need a transformer/middleware, or an integration, to process it first. We do however, have a public Adventure 1.0 API lab where you can create your own Webex Teams chatbot that processes webhook alerts from your Meraki org, as well as do other things including taking snapshots from motion alerts, MQTT real-time events, and more.
Solutions Architect @ Cisco Meraki | API & Developer Ecosystem
Not certain if you are still trying to do this, but there are several conversations where people have used Flow to receive the webhook and then format the data and send it into Teams. Still somewhat convoluted, but at least not going to a third party app outside of the MS environment.