pitch to an opportunity
An application is a creator's response to a brand's posted opportunity; it is the same object as an offer, born already linked to the brand's campaign, and becomes a booked flight if accepted.
When a brand posts an opportunity, a creator applies to it. An application is that response, and it is the same object as an offer, born already linked to the brand's campaign.
Applying is free and never uses a creator's pitch allowance, because the brand solicited it. If the brand accepts, the application becomes a booked flight at the rate the creator applied with.