In these cases you where you have received two orders from the same customer -
they are unable to cancel from their phone but if you or the team notice it you can cancel the second order as it comes in.
However if you don't realise that this has happened you can always credit their account on your posBoss till by going to Accounts & Vouchers and press Mobile.
Locate their account & pay off the double charged amount by entering the amount of the order & selecting to pay by Clear Balance - which removes that money from posBoss.
Here's an example
Two orders come through for $12.50 for Bob at posBoss, but the second order was a double up.
Both have been charged to the account but you need to remove $12.50
On the posBoss iPad till app - press the settings button and press Accounts & Vouchers. Press the Mobile tab. Scroll down or search for Bob. Once located, select Bob's account. You will see both orders there. Press Pay Account and then the Partial button. Enter in $12.50 then press the Clear Balance button to remove that amount from posBoss and the cash up.
This removes the amount from the account (and posBoss) Your stock movement will be impacted as there is a double entry. This can't be changed.