No, you can only use Athletics.app if you purchase a competition license in advance.
Unfortunately, you cannot get a refund if competitor attendance is disappointing.
You can, however, first purchase a license of, say, 150 competitors and during the competition via iDeal purchase an additional license of, say, 50 competitors, giving you room for 200 competitors in total. You can increase the license several times if needed.
This has been automatically translated into English