How can I add a line item on an invoice between items already entered on the invoice.

Welcome to the QuickBooks Community, aztecmascon.

I'll ensure you can smoothly add a line item on an invoice between items already entered on the transaction in QuickBooks.

I recommend clicking the Green Plus icon and selecting the one beside the second entered item. This allows you to insert a new line item across already-added products and services. I added screenshots below for visual reference.

In case you need steps on how to personalize and add specific info to your sales forms, you can read this article: Customize invoices, estimates, and sales receipts in QuickBooks Online.

Feel free to post here again if you have further questions about your invoices or other QuickBooks-related concerns. I'm always here to help you, aztecmascon. Stay safe!