Will re-posting an order create a duplicate invoice?

No. When you post an order again, the app updates the invoice it already created in Xero rather than making a second one. It keeps a record of which invoice belongs to which order, so posting the same order twice, ten times, or again after you have changed a setting all end up in the same place.

That is why re-posting is the normal way to put an order right. Change the setting that was wrong, post the order again, and the invoice already in Xero is brought up to date.

The one case where a second invoice can appear

Switching between individual invoices and summarised invoicing changes how orders are grouped, and orders sitting either side of the changeover can be picked up both ways. An order can end up with an invoice of its own and also be counted inside a summary covering the same period. The same thing can happen in reverse if you switch back.

It is limited to the changeover itself. Once every order is being handled the same way, the grouping settles down and it stops.

Checking where each invoice came from

Open each invoice in Xero and look at History & Notes at the very bottom. Xero records there what created the invoice, so you can see straight away whether both were posted by the app or whether one of them was entered in Xero by hand.

What to do if you find one

Tell us rather than tidying it up yourself. Email help@hyvelabs.co with your shop URL and both invoice numbers, and we will work out which one should stand and correct the order's invoice.

Please don't void or delete either invoice in the meantime. Once an invoice is approved in Xero it is part of your books, and removing one leaves its payment, and the order it came from, pointing at something that is no longer there.