Solved
I have marked an invoice paid by accident - how do I change this?
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Simply delete the corresponding payment entry.
On the invoice entry screen, top right corner, you will see something like...
PAYMENT STATUS
PAID
1 payment made on 01.11.2019
Click on the '1 payment' link to go to the payment entry.
At the bottom of the payment entry screen, select MORE, the DELETE.
(or edit the payment entry to show the correct invoice paid)
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