A straightforward way to invoice agreed fixed prices per period (for agreed maintenance for example), is to prepare the billing documents in the Work Order module. The example below illustrates contract invoicing taking place on the 1st and 25th of each month.

For each work order (one for each day, 1st and 25th), order lines are created for each month. For all order lines, the options for "Show in mobile" and "Chargeable" are deselected.

When invoicing, select the work order for the relevant day (1st or 25th), mark the order line for the month you want to invoice as Chargeable and create an invoice from the work order.
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