Hello! This answer is for V.14

The POS app doesn't work as the Sales app. In the POS app, first comes the payment record and after it the ticket is created (and the invoice if wanted).

With a standard shop it's possible to pay with more that one payment method (for example: pay 50% with bank card and 50% in cash), but it's not possible to create partial invoices. It's necessary to add the total payment to create the invoice.

If you configure the POS as a Bar/Restaurant, you have the option of Bill Splitting. 

How this works? In case that an order has more than one product, it is possible to pay them in different invoices (and with different payment methods). What its not possible is to pay part of the price of one of the order's products, its mandatory to pay at least the total amount of one of the products to get the split invoice.

Hope this helps you!