Open the gig from Gigs. Under The band each player shows one of:
The line above the list counts them, for example 3 confirmed · 1 waiting · 0 turned it down.
If a player texts or calls you instead, press Mark in or Mark out next to their name. Marking someone out sends you the same email as when they say no themselves.
Players can change their own answer on their page up to the day of the gig.
The Still open box lists sections under the minimum and lead chairs that haven't said yes. No gaps means you're covered. The minimums come from Usual band size on your band page. A part nobody on your roster plays is never counted as short, so a 4-piece won't be told it needs horns.