I'm here to share some tips on how to send an invoice to your customer without counting it as double revenue, @Annjay.

I suggest you provide a customer statement with the invoices from the last three months. This prevents you from sending another invoice that will result in double revenue. 

You can choose either a Balance Forward, Open Item, or Transaction Statement. It's like sending them a gentle, detailed reminder about the upcoming invoice deadline.

Here's how:

1. Go to the Sales menu and then Customers.
2. Select the checkbox for the customer you want to make statements for.
3. In the Batch actions dropdown, select Create statements.
4. In the Statement Type dropdown (Balance Forward, Open Item, and Transaction Statements).
5. Select the dates for the statements and the date range.
6. Review the customer's email addresses.
7. Click on Save, Save and Close, Save and send, or Print or Preview.

For more information about the different types of customer statements, viewing, and customizing them refer to this article: Create and send customer statements in QuickBooks Online. 

After sending the statement and receiving customer payments, see this article on how to record it in your account: Record invoice payments in QuickBooks Online. 

Let me know in the Reply section below if you still have questions about customer statements or anything else about invoices. Have a great rest of the day!