Reactions in the UI are not yet supported: please see here for details.
You may express a structured opinion on data you see on ThreatExchange by *reacting* to that data. For example, to express an opinion about descriptor `952030561511282` using the API, append your access token and issue a POST to:
To retrieve the reactions of everyone else, append your access token and issue a GET to:
my_reactions field will show your own reactions, and the
reactions field will be a map from the possible ReactionType to the apps that reacted with that type. If there are no reactions, the field will be empty.