Classes functionality will work on handling project invoices, @lkoronowski-kitc. Aside from that, I have suggestions to achieve your task. 

I'm happy to help you with how to bring your invoices to your QuickBooks Online account. This way, you can manage them without a moment's delay. 

I'd recommend contacting your old software support and asking if they have availability to add a Project field. If they don't have an alternative, I'd suggest utilizing a third-party app or manually entering them in QBO as my colleague mentioned above. 

Here's how to look for an application that is compatible with QBO: 

1. Go to the apps.intuit.com and choose your country in the drop-down. 
2. Locate an appropriate app in the list. 
3. Follow the on-screen instructions. 

For classes, you'll need to turn on the feature first to use this. Let me show you how: 

1. Go to the Gear icon on the upper right side. 
2. Select the Account and Settings tab. 
3. Choose Advanced, then turn on the radio button in the Categories section. 
4. Click Save, then Done.  

After that, let's create a classes list by following the steps below: 

1. Select the Gear icon again and select All Lists. 
2. Choose Classes and hit New. 
3. Enter a Name and click Save.  

Read through this article for more knowledge: Create and manage classes in QuickBooks Online.

Once done, you can manually add the invoices and link them to classes. Then run a Project Profitability report to supervise your transactions. See the screenshot for more details: 

Moreover, check out these articles below to know more about handling class tracking and projects in QuickBooks: 

• Get started with class tracking in QuickBooks Online.
• Projects FAQ

Don't hesitate to notify me if you need further help with QuickBooks projects. I can lend you a hand anytime. Have a great day.