Hi - you can create a new account using the first G/L account number available such as 1001. I usually call it 'Suspense Account'. Classify it as a bank. I like it to be the first one showing on the balance sheet as a reminder to ensure that account is at a nil balance.

Then you can 'pay' your vendor using this as the bank account - chq nbr can be something like 'Pay???Customer'. Then show a deposit using same Suspense Account to your customer using receipt nbr something like RecdFrom???Vendor'. You would use the same date for both supplier and customer payment.

When you look at the Suspense Account general ledge you will see both a credit and a debit of same amount bringing the balance of the Suspense Account to nil. 

The suspense account is handy to enter items that you are not sure where to place it on the income stmt - you can then go back later to change it to the correct G/L acct nbr.