I can't find where I can charge credit card in the app

There are various way you can charge a credit card using QuickBooks Online Mobile App depending on your device, Master.

If you're using an android device, you can follow these steps 

1. Fill out the necessary details on your Sales Receipt or in the Receive Payment screen.
2. Choose how you want to enter the credit card information:

• Swipe: Swipe the card through a card reader and have your customer sign with their finger.
• Scan: Select Scan card info, position the card, scan according to your device, fill in any missing information, then select Done.
• Key enter: Select Enter card info, enter the credit card number, expiration date, CVV code, and customer billing ZIP code, then select Done.

        4. Select Charge.

        5. Click Email to send the sales receipt or payment to your customer.

You can check out this article for more details: Accept credit card payments using the QuickBooks Online app (Android only).

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.