how do I turn on the online delivery option and save it?

You can enable the feature in your settings to show receipts on your customer's email, dave258.

Here's how to turn on the Online Delivery option: 

1. In your QBO account, go to Account and Settings and click Scroll down and click the Online delivery option.
2. From the Additional email options for invoices drop-down menu, choose Online invoice.
3. One done, select Save and then Done.

You can also modify the look of your sales forms; for further information, refer to this article: Customize invoices, estimates, and sales receipts in QuickBooks Online.

In addition, I have provided this resource to assist you in manually tracking invoice payments and keeping your records accurate: Record invoice payments in QuickBooks Online.

If anything comes to mind, you can always leave them in the comments below. We're here ready to help. Keep safe.