The new mobile app does not allow for choosing service dates on invoices for each line item

Thanks for getting in touch with the Community, oasislandscapeau.
 

I can certainly understand how an ability to add service dates on invoices in your mobile app could be useful and have submitted a suggestion about it as of today.
 

You can also submit your own feature requests while signed in.
 

Here's how:

1. Use the Gear icon, then go to Feedback.
2. Enter your suggestion(s) in the Have feedback? window.
3. If necessary, attach a file with your Camera icon.
4. Select Next.
   
   

Your feedback's definitely valuable to Intuit. It will be reviewed by our Product Development team and considered in future updates. You can stay up-to-date with the latest news about your product by reviewing Intuit's Product Updates webpage.
 

As a workaround, you can add service dates to line items on invoices while using QuickBooks in a web browser. To do so, you'll need to confirm your Service date option is turned on in the account settings:
 

1. Use your Gear icon, go to Account and settings.
2. Access the Sales tab, then go to Sales form content.
3. Turn on Service date if it isn't active yet.
4. Select Save, then Done.

I've also included a detailed resource about working with invoices which may come in handy moving forward: Customize invoices
 

If there's any additional questions, I'm just a post away. Have a great Monday!