This is likely because the project defaulted to a Rate Card with $0 billing hourly rates when it was first created- possibly "Internal" or Standard if you have not added an role hourly rates.
At the moment, changing the Rate Card subsequently will not automatically update the Project Rates - you would have to update the Project Rates manually.
💰 How to update the Project Rates?
Click on Manage>Rate Cards.
Click on Create a New Rate card.
Add the relevant hourly or daily rates.
Return to your project and open the Budget modal by click on 3 dots and selecting Edit Budget.
Click on the second tab- Project Rates.
Click on the rate card to change it to the one you just created.
7. Then, click on the arrow to apply the project rates.
This will update all rates and display revenue correctly. You can also edit these rates if you've caught an error or only one role rate has changed.
Please note that updating a rate card will NOT automatically update all projects using that rate card. You'll need to click on the arrow for each project to apply the changes.