Hello @userdaskin! Hope you're having a great week, happy Friday. :) I can definitely explain the options you have for invoicing in QuickBooks Online. 

When you create an invoice, you can only enter in one customer/project per invoice. There is a "save and new" option that will save the invoice you're working on, and then open up a new one for you to work on.

If you have QuickBooks Online Advanced, there's a new feature called "batch transactions" that allows you to enter multiple invoices at once. Here are the steps for that:

1. Select + New.
2. Select Batch transactions.
3. Select the Add (+) button to create a new blank invoice. Each invoice you add gets its own numbered row.
4. Select any field to enter info for each invoice.
5. When you're done, select Save.

Here's the full article with other information on this feature: Create and send multiple invoices in QuickBooks Online Advanced.

If you have any further questions, please feel free to reply to this post. All of us here in the Community are happy to help!