Spares are only eligible to check-in for games once they have been invited to an event in RosterBot.
Prior to being invited they will be told they are ineligible to check-in for these events.
Spare players will be invited to an event automatically by RosterBot when:
1. The Spare toggle is turned on (set by a manager)
2. The event has not reached it's minimum number of players by the time the Spare invitations are scheduled to be sent.
Once your team's Spares have been invited, everyone on the team (Spares and Full-timers) are treated equally and can take any remaining spot for that event.
A manager can also manually invite specific Spare players by clicking the 'Invite' button for a certain player on the Event page.