Once this is applied to the Galaxy S6 Edge phone does the headphone work?
I use my phone for processing monetary transactions via Square. Will the Square plug-in work with this external battery case in place?
No, the square only works if the aux jack is flush with the phone casing. The only way you would be able to access the port like normal is to have an extension for the aux, and maybe... just maybe the Square can plug into that, and still read the card data and process it to the app/ phone