Hiya,
This issue has probably been day one of Matillion Webhook component.
https://matillioncommunity.discourse.group/t/matillion-etl-version-1-48-is-here-featuring-webhook-post-component/1191
At least the screenshots looks quite the same as your issue :) Didn't go further with this one at that point. But would be interesting to actually have these pretty formatted Teams-messages popping from Matillion.
It might be a bug, due the value field doesn't really accept any values.