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Select the events you would like to invoice by ticking the boxes on the right hand side of the table for the appropriate events, and then click 'Export' (or 'Send to accounting package' if you use an online accounting package: for information on how to configure you accounting pack, go here).
When selecting multiple events for a single client, the system will group those events by client and purchase order number (if entered). This means if you have selected 5 events for one client, only one invoice will be raised, which will contain the 5 events. In the instance a purchase order has been entered (eg. PO123) for 2 of those events, you will have two invoices raised - one with the purchase order number PO123 with 2 events, and another with the remaining three events without a purchase order number specified.
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