activity feed notification cards character limit?

egetunca 

I don't know how many characters you can send to the API call, not sure if that's documented somewhere. What I do know is that Teams will only shows 150 characters from your preview text. This is documented on the page of the API call itself: https://docs.microsoft.com/en-us/graph/api/userteamwork-sendactivitynotification?view=graph-rest-1.0&tabs=http&WT.mc_id=M365-MVP-5003400

Hopefully this answers your question (and thanks for the tag ChrisHoardMVP !).