Create Order REST API

New to Shopify. I was posting to the following URL /admin/api/2021-10/orders.json with following body to receive a response"order": “Required parameter missing or invalid”. How can I identify what is missing here? I was referring to https://shopify.dev/api/admin-rest/2021-10/resources/order#post-orders

{
	"order": {
		"line_items": [{
			"title": "Clicky Keyboard",
			"price": 99.99,
			"grams": "600",
			"quantity": 1,
			"tax_lines": [{
				"price": 1.0,
				"rate": 0.01,
				"title": "Keyboard tax"
			}]
		}],
		"tax_lines": [{
			"price": 6.0,
			"rate": 0.06,
			"title": "State tax"
		}]
	}
}

Below body also returned similar error

{
	"order": {
		"line_items": [{
			"variant_id": 447654529,
			"quantity": 1
		}]
	}
}

The above issue got resolved when content-type header application/json was added