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To clear the hold and release any items in it, cancel the sale after pulling the sale out of hold status.
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Invoices can end up on hold in two ways: manually or automatically.
Manually, the hold will be displayed in black text, this indicates that a user clicked the Hold button on the cash register, placing the invoice on hold.
Automatically, the system has placed the transaction on hold itself. This can happen for any number of reasons: power outage/brownout, networking issue, computer issue, user forced the software closed or forced the power off for the computer, etc. The system does this automatically to prevent losing transactions in case of accident or technical difficulties.
Your system can be set to not allow closing the register with open holds, but note that this is a flag setting and only applicable on transactions created *after* the flag is set: prior holds will not prompt the user to close them at the end of the day.
An invoice on hold with no products, a zero value and sometimes no other information, but is prompting that it has a payment on it, indicates that a user tried to close a hold/sale improperly after a payment was placed on it. The correct way to remove such a hold/sale with a payment on it is to first remove the payment and *then* cancel the sale.
If done on the day the invoice was rung up, you can just add any item to the invoice, remove the payment on the payment screen and then cancel the sale.
To correct this after the original date of invoice, you'll want to run the "Invoice Lines Deleted (xls)" report in the Cash Register reports module, and then search for the invoice in question. This will give you the products that were on the invoice originally. Add those items back to the invoice and finalize the sale, then do a refund of the invoice to balance your numbers for the day.
If you want to review your current open holds without looking for them individually, you can run the "Open Invoices (xls)" report in the reports module of the cash register, this will show you all of your current open holds. Please note however that because this displays all open invoices, if you run it during your business-day it will also be displaying transactions that are currently in process in the store, since there's no way for the system to differentiate between a sale-in-process and a brand new hold