magento2 – how to get custom attributes in rest search api?

In order rest api http://127.0.0.1/mag/index.php/rest/V1/orders/1
it shows custom attributes

 "payment_additional_info": [
        {
            "key": "method_title",
            "value": "Check / Money order"
        }
    ],
    "applied_taxes": [],
    "item_applied_taxes": [],
    "preorder": "1"

while in order search rest api http://127.0.0.1/mag/index.php/rest/V1/orders/?searchCriteria[filter_groups][0][filters][0][field]=entity_id&searchCriteria[filter_groups][0][filters][0][value]=1

it did not shows custom attribute

"payment_additional_info": [
                {
                    "key": "method_title",
                    "value": "Check / Money order"
                }
            ],
            "applied_taxes": [],
            "item_applied_taxes": []
//did not show preorder which is custom attribute