Also, there's a possibility that you've received the payment into your Undeposited Funds account instead to your business checking account. In this case, you'll need to process bank deposit. To do this, you can visit this article for the detailed steps on how to Record Bank Deposits in QuickBooks Online.
If you need further assistance with the steps, I encourage you to contact our QuickBooks Online Support Team. They have additional tools to pull up your account and do a screen share.