For-this-purpose-the-Lender-is-authorised-to-use-all-or-any-part-of-any-such-credit-balance-to-buy-such-other-currencies-as-may-be-necessary-to-effect-such-application-what-is-credit-balance-in-this-sentence

Credit balance refers to the amount of money that is available in an account after all debits and credits have been accounted for. In this sentence, it refers to the funds available in the borrower's account that can be used by the lender to purchase other currencies necessary for the transaction.