Dynamo Kyiv levelled against Barcelona through a Kedziora header, but the goal was ruled out because the cross, from the corner, had gone out of play then came back in. Koeman's men had their guard low.
Kedziora could have given hope to Dynamo Kyiv in their Champions League match against Barcelona, but it wasn't to be because the cross had gone out. That's what the referee understood just before he headered and beat Ter Stegen.
The Barcelona keeper made a false start and was unable to cover enough to prevent his opponent from sending the ball into the net. The defence was not fine either, which allowed the visitors to move very free and look for the ball without much pressure.
They responded at a time that Barcelona were sleeping. The hosts went in front thanks to a Leo Messi penalty, but after they were going to less and less and leaving spaces for the Ukrainians, who, like it couldn't be any other way, made the most of it.
In fact, Ter Stegen had to appear some minutes later with a saving foot so that a counter from Dynamo Kyiv didn't end in a goal. Had the goalkeeper been beaten, there would have been no chance of the goal being disallowed and Barca would have been in trouble.