We can send your invoice by clicking the Review and Send button placed at the bottom of the transaction window, David. Since you're not seeing the option, we can perform browser troubleshooting steps.

Let’s start by clearing your browser’s cache and cookies for a fresh start. This step can help eliminate unexpected behavior that prevents QuickBooks from displaying the option to send invoices.
If the issue persists, you can consider using other supported browsers to further isolate the problem.
Once you've completed these steps, you can refer to this article on marking your invoices as paid after you have actually received payment from your clients. This will help keep your records accurate: Record Invoice Payments.
If you need further assistance with managing invoices or any transactions in QuickBooks, feel free to reach out. The Community is just a post away to help you.