"To complete the transaction" means to finish the process of exchanging goods, services, or money between two parties. It signifies reaching the end of a business deal or agreement. Full definition
Whether it is seller or buyer, I will do what is necessary to complete a transaction in with the utmost professionalism and are. (zillow.com)
When ready to purchase, users have the option of completing the transaction online or talking directly to a licensed agent. (comparisonmarket.com)
Rather, under the terms of the assignment document, the original buyer can remain liable to go through with the contract if the new buyer does not complete the transaction with the builder. (remonline.com)