If you are a partner and want to use the API as a particular merchant, you must authenticate your account by passing an additional header X-Razorpay-Account with the merchant account_id as the value.
var instance = new Razorpay({key_id: '<your_partner_key>',key_secret: '<your_partner_secret>',headers: {"X-Razorpay-Account": "<merchant_account_id>"}});instance.orders.all().then(console.log).catch(console.error);