They should be more careful in the second half and find a way in which they can use to win the match and not allow Monaco to defeat them if not it will be a bad start for them this season.
Second half is going to be rough for the Barcelona team, most definitely. Monaco has already shown the readiness to win this match, if not for anything, to prove it to Barca that they can hold them tight and that the first win wasn't just by a mere luck.
The scenario of the match changed completely after the referee showed Garcia a red card. Monaco is not a weak team. With 10 players, it will naturally be a tough task for Barcelona to beat Monaco in their home match. And Monaco managed to take the lead early in the match. However, Barcelona was able to equalize the match with Yamal's excellent goal. However, in the second half, it was more difficult for Barcelona's defenders to resist Monaco's attacks.
Since Barcelona are playing with 10 players, naturally Barcelona have to play with some defensive tactics. Barcelona players are not able to attack much. However, Barcelona players continued to try to score. Both Barcelona and Monaco are playing well. I would say both teams still have equal chances to win.