Direct offers
Negotiate privately with another club for a player who isn't on the market.
A player who's under contract and not listed for auction can still move: it just takes a private negotiation between the two clubs, instead of the whole league bidding.
What an offer can contain
An offer can include cash, players, or both, up to 2 players per side. Player-plus-cash works in either direction: you can sweeten an offer with cash on top of a player, and a seller can ask for cash back the other way. The seller always sees the offer's total value up front.
Expiry
An offer that isn't accepted, rejected, or countered expires after 48 hours. The recipient can also counter with a different split of cash and players instead of a flat accept or reject.
Why an offer gets rejected
Common rejections come with a clear reason: the buyer can't afford it, accepting would put the buyer over budget, or the cash split would leave someone's side negative. Nothing gets silently declined.