On the transfer market you can buy and sell players.
Sell players: You can put players on the transfer market at any time. Kickbase always gives you a bid after about 1 hour (but it can take longer), the other managers can of course also make you an offer. If you like an offer, you can accept it immediately. After accepting the offer, the player will be transferred and the amount will be credited to your account. Transfers can not be reversed!