Depending on when you signed up for 17hats, you may have connected to Square as your merchant account for processing Invoice payments.
You will need to enter a location for your business directly at Square if you haven't already done so (it does not need to be a physical address). To do so at Square, navigate to 'Account > Business Information > Locations' first and then you should see that as an available option from the dropdown menu within your Invoice Options at 17hats:
*Please note, Square is not available in all accounts
KeywordSearch: Integrate, Square, SquareUp, Pay with Square