If you notice the ability of a card is not working as described in its tooltip, please make sure that you meet all the requirements for the ability to trigger.
For instance, if you play a unit that can damage enemy units and it has Reach: 1 requirement listed in its tooltip, note that you won't be able to target enemy units in the Ranged row. If, in such situation, the opponent has units only on the Ranged row then the card's ability won't trigger at all.