Create an order and apply Application discount

[jh_zzz]

We are a wholesale company, we want different price for different quantity, actually we have upgraded to shopify plus, but seems the wholesale front shop need run in an standalone site, this is not we wanted.

From this article https://shopify.dev/api/examples/order-editing, I know we can apply an application discount for an exist order, and I have tried it works.

Because it can only apply to exist order, so we:

1. Use REST api to create an order with one item （cannot create an order without line item through REST api, it must have at least one line item）

2. Use order-editing api add more items with discount according the quantity.

The problem is:

The orderEditAddLineItemDiscount api only can apply  to the line items added by order-editing API, can't apply to the  line-item created by REST order api, or manual create items.

So for first item, we cannot apply discount for it (we don't use discount code because our discount is dynamic according the quantity user selected)