We have built an app to allow syncing stock of products to Shopify from our ERP system. We download orders from Shopify and then when they are fulfilled in our ERP system, we fulfil them in Shopify using the API.
We are setup as a fulfillment service and manage the products' stock.
Some of our customers would also like to use the Shopify POS, but we've been told that the Shopify POS is refusing the sale as the item is showing as out of stock (as the stock is tracked in our location, not by Shopify). One customer contacted Shopify support and was told "third-party app location used for inventory tracking are not compatible with the POS app".
How can we resolve this? Is it possible for us to sync stock to our own location as well as Shopify's so that the POS can make sales? Or make the POS just consider our stock location? Surely it can't be impossible to sell on the POS and the e-commerce website when the stock is managed by a fulfillment service?