If you're not able to start a match in the event, note that this is an expected situation that happens in either of the following scenarios:
You either have another match, official match or friendly, that is about to start, or
you are trying to play the match close to our daily maintenance (usually around 3-6am CET).

If you see the following message please just try to play your match later on, as it is stated: "Please try again in a few minutes. You may not be able to play this game because your players are already playing another game or are about to play one. The game could also be undergoing maintenance."