You can select a preference in the Preferences window - Stock view that will allow you to have the balance of the value and the on-hand quantity of stock item be less than zero. That is, you can record a transaction in MYOB Accounting that will result in negative stock.
When you choose the preference Allow the sale of items with insufficient quantities, you can record a negative stock transaction. A negative stock transaction is a transaction that would result in an item with an on-hand quantity and a total value less than zero.
Transactions that would result in an item with a negative or zero value with positive on-hand quantity or the alternative -- a positive value with a negative or zero on-hand quantity, will not be permitted.