question

There are two types of discounts to consider here: Line Item level Discounts and Order level Discounts. When requesting an Order with the REST API, you will get a list of the Order level Discounts applied (only if there was at least one Order level Discount applied). The Line Item discounts are not included.

Additionally, you can expand nested fields. For example, below I am expanding the Discount and LineItems Fields of the Order, but I am also expanding the Discounts Field of the expanded LineItems Field (lineItems.discounts). (See our docs for more information on expanding multiple fields, as well as nested fields)

Example Endpoint to get both Order Level discounts, as well as Line Items discounts in a single call:
https://apisandbox.dev.clover.com/v3/merchants/{mId}/orders/GMZQRZ6DE9NHP?expand=discounts,lineItems,lineItems.discounts

Example response:

{
    "href": "https://sandbox.dev.clover.com/v3/merchants/{mId}/orders/GMZQRZ6DE9NHP",
    "id": "GMZQRZ6DE9NHP",
    "currency": "USD",
    "employee": {
        "id": "4HKYYG4YD8E6E"
    },
    "total": 2428,
    "taxRemoved": false,
    "isVat": false,
    "state": "locked",
    "manualTransaction": false,
    "groupLineItems": true,
    "testMode": false,
    "payType": "FULL",
    "createdTime": 1536947864000,
    "clientCreatedTime": 1536947864000,
    "modifiedTime": 1536948293000,
    "discounts": {
        "elements": [
            {
                "id": "XZ1FDCAS2C3BT",
                "orderRef": {
                    "id": "GMZQRZ6DE9NHP"
                },
                "name": "10% Off",
                "percentage": 10
            }
        ]
    },
    "lineItems": {
        "elements": [
            {
                "id": "TGJ1B5QX98YG8",
                "orderRef": {
                    "id": "GMZQRZ6DE9NHP"
                },
                "item": {
                    "id": "VDR2QYCABGV9Y"
                },
                "name": "Moogle Plushie",
                "price": 1999,
                "itemCode": "1",
                "printed": false,
                "createdTime": 1536947864000,
                "orderClientCreatedTime": 1536947864000,
                "discounts": {
                    "elements": [
                        {
                            "id": "MBZD478MTW462",
                            "orderRef": {
                                "id": "GMZQRZ6DE9NHP"
                            },
                            "lineItemRef": {
                                "id": "TGJ1B5QX98YG8"
                            },
                            "name": "15% Off",
                            "percentage": 15
                        }
                    ]
                },
                "exchanged": false,
                "refunded": false,
                "isRevenue": true
            }
        ]
    },
    "device": {
        "id": "****************************"
    }
}

The above order has an order level discount of 10% and a Line Item which as an individual 15% discount.

I have submitted a ticket to make this clearer in our Docs. Thank you for pointing this out for us!