Largest youth league in the US with over 4400 teams, and the games are all schedules through GotSport. Numerous other leagues (Florida Club Leagues for example, also very large) and numerous tournaments use it.

Last year, I spoke with GotSport’s chief of development (not the exact title, but the guy who decides what and when things happen) and his words were more or less like this: “ Never in hell will be providing APIs to our schedules” So, don’t hold your breath for this to happen.
I fail to understand being so closed-minded on APIs. Hopefully his mind changes soon.