Good day, @ranee624.
Once your customer received and read the emailed invoice you've sent. It will show viewed in your Sales tab.
Here are the different statuses of an invoice found in QuickBooks.
- Sent: Your invoice was sent using one of the email options in QuickBooks.
- Viewed: Your customer already received and opened the email.
- Paid: You entered a payment for Invoice in QuickBooks. The history displays partial and full payments.
- Deposited: You record a payment deposit in QuickBooks.

I'll be sharing with you our page about income and expenses in case you need some reference in the future.
You can always find me here if you have any other concerns. It'd be my pleasure to help. Be safe.