This is the making of the contract between the parties.
The quickest and easiest way to see if a contract has exchanged is if it’s dated. There are two identical contracts, one signed by each party and the contracts are exchanged so that each party holds the contract signed by the other party.
The deposit is paid at this time and the contracts are dated. It is at this point that the parties are bound to the transaction and the contract contains all the conditions of the sale.