An Invoice that is created at the POS system does NOT have an order_id, therefore it can’t be paid with the Payments API. How do you pay the Invoice in this case with the Square API?
Unfortunately, the ability to pay an invoice that was created at the POS isn’t currently available with the Invoices API. We’re constantly working to improve our features based on feedback like this.
This is really disappointing! How am I going to explain this to my customers???