A party to a contract will be discharged from further liability:
a) If he has performed his obligations.
b) If he makes a valid offer (or 'tender') of performance which the other party rejects.
Money debts will be discharged if the debtor shows, not merely that he tendered the correct sum upon the date on which it is due, but also that he was ready and willing to pay up to the time (!) that the creditor brought his action for the recovery of the debt.