How do you add/include an invoice when sending out customer statements?

Thanks for posting here, @zengen89,

I can share some insights on how you can send your customer's statement and invoices together.

At the moment, sending customer statements along with their invoice in one email is not yet available. QuickBooks is designed to send invoices and statements separately, regardless of the customer or email address on file.

As an alternative, you can download the statements as a PDF file. Then, you can attach it to the invoice and send it to the customers.

To download the statements as PDF:

1. Tap the Sales menu and select the Customers tab.
2. Mark the checkboxes for the customers you want to make statements for.
3. In the Batch actions dropdown ▼, select Create statements.
4. Select a Statement Type.
5. Pick the dates for the statements and the date range.
6. Select Print or Preview.
7. Click the Download or Print icon and save it as a PDF file.

To append these attachments to the customer invoices, follow the steps below:

1. On the invoice, scroll down to the Attachments box.
2. Click the box showing Drag/Drop files here or click the icon.
3. Pick a file from your drive then save the transaction after.
4. Make sure to click the Attach to email option.
   

Once the client receive the invoice on their email, they will see the attachment above the invoice link. See this:

Refer to the steps here to learn more about this feature: Attachments in QuickBooks Online

If you have any more questions about statements and invoices, please let me know in the comment. I'll be more than happy to share some insights about QuickBooks topics. Have a nice day!