Some events accept petitions (an athlete asking to compete at a level they have not qualified for) or alternates (a reserve entry). Where they are offered you choose the type at the start of registration.

These entries go to the event director for a decision. At checkout your card receives only a small temporary authorization, not the full fee - you are charged when the director approves.

You are emailed when the decision is made. A declined entry is not charged.

On a meet sanctioned by USA Gymnastics you do not choose the type at the start. Each gymnast on your reservation has its own Petition or Alternate button on the Alerts page, which sends that one athlete through and leaves the rest of the reservation for the normal Process button. See Entering one gymnast as a petition or alternate.