You can show a payment for a customer with store credit/ gift card via POS by following the steps below:
From Shopify POS, tap Store > Payment types.
Tap Gift Card.
Tap the toggle buttons to activate one or both of the following options:
Shopify has a guide for this going through the details step by step which you can read here.
We are trying to put all of our stores on Shopify ASAP, but we do offer in-house charge accounts. There is a company called Invoiced that needs an API with Shopify in order for the charge account to function properly. Is there someone who could build this integration for us quickly. We need something to happen very quickly. Shopify just needs to check invoices to make sure the customer has room to charge so they are not over their credit limit. Thanks, Will