If you’re using iOS, you can enable the Tap to Pay option to accept payments for invoices on the go without setting up a card reader. For complete instructions, please refer to the Tap to Pay in the QuickBooks GoPayment or QuickBooks Online mobile app (iPhone only) section in this article: Process payments in the QuickBooks mobile and QuickBooks GoPayment apps.
Let me know if you need any additional help managing payments using the mobile app. Support is always available.