Collectible Card Game Headquarters

Let me explain the situation:
Opponent attacks with a creature and I have a Condemn (or a Path to Exile -> its similar) in hand.
In the declare attackers step the game does not let me to do anything and in the declare blockers step the condemn is purple-bordered but I can't cast it (the only thing that lets me do is declare some blockers although the instant-speed cards are purple-bordered).
I would be grateful if someone replied to me in order to fix this bug
Thank you

Not really a bug. You're most likely using F5/F9 (or the equivalent on-screen buttons) to skip to your opponent's end of turn or your next turn in order to not have to keep pressing "Done" on every single phase and action, and in those cases XMage will only stop on the declare blockers step.

You can't actually play anything while declaring blockers, you can do it before and right after, though.

What you want to do in those cases is either press F3 (cancel skip) if you know you're going to want to play something soon, or do it while at the declare blockers step, so that after you declare your blockers (or none at all) the game actually stops on your priority and let's you play your instants or abilities before damage is done.

Thank you! I was using the F5 button. I actually thought of the F5 as the problem.