If you get the Reversed Participants notice in the bet card, it’s just to let you know that the order of the participants might not be the same on both bookmakers.

For instance, on Pinnacle it might be:
Korea – Spain

And on Betfair it might be:
Spain – Korea

This could happen for instance if a match is played at neutral ground and no team is the home team. When the participants are reversed, you must (as you always should be doing) make sure that you back the correct players on the correct sportsbook, as it might be confusing when the participants do not have the same order at both bookmakers.