Sometimes our games don't get quite enough players for a full session! Maybe you need at least 3 players, but you only have 2 signed up at start time.
Players in scheduled sessions will be charged even if the minimum player count is not met.
By assuming a charge will go through, this gives you as the GM more choices for sessions with low player counts.
You can choose to cancel the session and refund the players. Or, you can play with the players who are able to attend (like running a one-shot, or readjusting the story for the number of players you do have).
Whatever you choose to do with your session, just make sure to communicate with your players what you'll be doing.