Processing_method is blank (instead of manual)

Retired Boards Appdev Graphql Basics And Troubleshooting
1

I’m using the Shopify Admin REST API

I can create simple (prepaid) orders where payment is made through Razorpay/Stripe (In India)

However, when I try to create a COD order, even after specifying the transaction.gateway as a custom payment gateway that I have created in my store, when I create the order, the response shows that processing_method is blank (instead of manual)

How do I ensure that processing_method has value of manual? In the Order object, it is a read-only attribute, so I understand that it cannot be set directly

My order object looks like this:

{
    "order": {
        "customer": {
            "first_name": "emm",
            "last_name": "kay",
            "id": "6133275590826",
            "phone": "+914244590110",
            "tags": "mobile_customer"
        },
        "test": true,
        "financial_status": "pending",
        "transactions": [
            {
                "kind": "sale",
                "status": "pending",
                "amount": 848,
                "gateway": "Cash on Delivery (COD)",
                "processing_method": "manual"
            }
        ],
        "line_items": [
            {
                "quantity": 1,
                "variant_id": "41891714629802"
            },
            {
                "quantity": 1,
                "variant_id": "41891714990250"
            }
        ],
        "phone": "+914244568890",
        "source_name": "MOBILE_APP",
        "tags": "COD, ORDERED_FROM_APP",
        "shipping_address": {
            "address1": "dsdsds",
            "address2": "jamshedpur",
            "city": "East Singhbhum",
            "company": null,
            "country": "India",
            "firstName": "Jane shipping",
            "lastName": "this test order",
            "latitude": 22.7740354,
            "name": "name in shipping address",
            "phone": "+911234567890",
            "province": "Jharkhand",
            "zip": "831006"
        },
        "billing_address": {
            "address1": "dsdsds",
            "address2": "jamshedpur",
            "city": "East Singhbhum",
            "company": null,
            "country": "India",
            "firstName": "billing address",
            "lastName": "this test order",
            "latitude": 22.7740354,
            "longitude": 86.1828047,
            "phone": "+911234567890",
            "province": "Jharkhand",
            "zip": "831006"
        }
    }
}