Hey james46,
Thanks for your post and welcome to the QuickBooks Community!
There is currently no copy line feature on the invoice, you would need to manually select the product/service on the separate line. If you have the the description and sales price entered in the product/service settings, this will then auto-fill the line with the data.
You can leave feedback for this feature by going to the Settings Wheel > Feedback, which goes directly to our developers who collate and implement suggestions based on customer demand :)