Howcto add a cash income transaction sale ?

You can use a sales receipt to record a cash income transaction in QuickBooks Online.

Here's how:

1. Click + Create and select Sales Receipt.
2. Choose your customer from the Customer dropdown menu.
3. Set the payment method to Cash and enter the transaction date.
4. Under the Deposit to field, choose your checking account for direct deposits, or select Undeposited Funds to group multiple cash payments together for a single bank deposit later.
5. In the grid below, select the items or services sold, enter the quantities, rates, amounts, and the tax.
6. Review it and click Save and Close.

For more detailed information, check this article for your reference: Create and send sales receipts.

Let us know if you have any other concerns.