LWAcceptance & Consideration

Dear Sir, In Acceptance , it is said in case of Household Fire Insurance Co v Grant that Postal rule applies (shares case) and outcome was "posting acceptance creates a ‘meeting of minds’, which created a binding contract" but defendant never paid for shares which he was allotted by letter. and in consideration it says "Consideration is a two-way thing in simple/parol contracts" so if defendant did not pay for shares , the transaction was not completed hence contract was not complete due consideration being one way only. please clarify if i am mixing up two different things. Thanks