Hello,
Sorry for the late answer.
You can get the matchup id from one of the following endpoints:
-/api/pinaculo/sports/{sport_id}/matchups
-/api/pinaculo/sports/{sport_id}/matchups/live
-/api/pinaculo/sports/{sport_id}/matchups/highlighted
-/api/pinaculo/sports/{sport_id}/markets/highlighted/straight
-/api/pinaculo/sports/{sport_id}/markets/straight
-/api/pinaculo/sports/{sport_id}/markets/live/straight
-/api/pinaculo/leagues/{league_id}/matchups
-/api/pinaculo/leagues/{league_id}/markets/straight
-/api/pinaculo/matchups/search?query={query_string}

Thanks.