We sign the papers at the exchange of contracts.
exchange of contracts
idiomThe point or stage at which a conveyancing contract comes into existence between negotiating parties for the carrying out of a disposition of an estate in land; usually requiring the payment of a deposit.
The buyer paid the deposit during the exchange of contracts, making the house purchase official.
Following weeks of negotiation, both parties finally reached the exchange of contracts, legally committing them to the transfer of the property.