Am I Ready to Send an Invoice in QuickBooks Online?
Welcome to QuickBooks Community, JakeV60.
We’re glad you’ve chosen QuickBooks to help manage your finances. Let me show you how sending invoices works in the program.
You need to first make sure you’ve added the email address of your customers in their profile. Then, as long as all the necessary purchase details are entered in the invoices, you can proceed sending them.
To add the email address of your customers:
Go to Sales in the left panel, then Customers.
Locate the name of the customer you need.
Choose the Customer Details tab, and click Edit.
Enter the email address in the Email field.
To send an invoice:
Open the invoice you want to send.
Click the Save and Send button at the lower right side.
If you want to send multiple invoices to one client, you can do it from the customer’s Transaction list. Here’s how:
Go to Sales in the left panel, click Customers.
Pick the customer you need, then select the Transaction List panel.
Put a check mark on the invoices you want to send.
Click the Batch actions drop-down, and choose Send transactions.
I've added an article below about Invoices for future reference: