In the main menu tap Documents and then Invoices

Select and tap the desired invoice you want to duplicate

Swipe up the lower bar to bring up the whole menu

Select Duplicate from the menu

A new window appears with all the data from the invoice

All data from the previous invoice apart from the dates have been copied to the new invoice. You can set your own date

Click on Save when ready - a new invoice with a new number is created

In the Documents section click on Invoices

A list of all invoices appears

In the list click on ... and select Duplicate
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The duplication icon is also visible in the invoice preview
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Select Duplicate

A window with an invoice appears - a new document has been created

All data from the previous invoice apart from the dates have been copied to the new invoice. You can set your own date

Click on Save - a new invoice with a new number is created