A broker employed to effect a sale does not earn his commissions by procuring one who enters into a contract with the principal which provides that the contract shall be void if the first of several payments of the price is not paid within the stipulated time. Ramsey v. West, 31 Mo. App. 676; Jones v. Eilenfelt, 28 Wash. 687, 69 P. 368; Edwards v. Baker, 180 P. 33, - Cal. App. - . See references under Sec. 307.