Hi Victor,
Adagio OrderEntry works the same as Accpac Plus in this regards. There is a company profile option on the 'System Options' tab called 'Credits on invoices' that must be selected in order to allow you to do as you requested. With this option enabled, you can enter a negative quantity shipped and also have a negative extended dollar amount.
You cannot enter a negative quantity ordered - this field should be left with a zero value.
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Regards,
Softrak Tech Support