Currently integrating Opsgenie with Microsoft teams using webhooks and not the MS teams integration because some customers do not wish to add the bot to their Teams environment, when the payload from Opsgenie is sent to Teams via webhook the error message received is,

Reason: 400 Bad Request: "Summary or Text is required."

This indicates that MS Teams needs Summary/Text included in payload, which is not a part of elements of Opsgenie's alerts. 

Hence a customisation to the payload would be great alternative.