Personal notifications

Hi. Excuse my ignorance as I've done a lot of research but was left unsure of the proper path. We have a web based product that organizations sign up for and every user in the organization, while going through web based onboarding chooses how they wish to receive notifications from us.

They can choose email, sms or in this new case, a Microsoft Teams Card. We want the least friction for an organization and especially the user to choose the Teams option.

What would you suggest is the best platform/delivery mechanism to allow a Teams admin to add us and the easiest way for the user to receive a card from us that has image, text and 3 personal-to-the-user buttons.

Is an app, webhook, or bot the easiest to distribute and how does the user add us to their teams app? In our case it's a single Card they would get twice a day based on the times they've chosen. Once the button is clicked, it is a personal /specific to the user url) http post/put. Thank you in advance!