How do I get the project number to show on the invoices I have created (but not billed)? So I can quickly identify which client belongs to which invoice. I have created invoices but cannot find the place to enter the project number.
There's no need to put a project number on an invoice- when the invoice is created the project it was created from is automatically attached to the invoice.
In the Invoices section (main left hand navigation) you should see the project name next to each invoice.
If it's the printout or download of the invoice that is blank where the project is listed that mean that the project itself didn't have a 'Billing Address' when the invoice was created. The project's 'Billing Address' is copied over to the invoice at the time the invoice is created- if it's blank you would need to fill that in yourself, in the invoice. It's always best to have a Billing Address already set up for each project (and supplier).
The Billing Address can be edited for the project in the Project Dashboard (click the name of the project with the edit/pencil button next to it). The Invoice Billing Address can be edited in the main invoice form, by clicking on it's number. Since you've already made the invoice you'll need to update the Billing Address in both the project and the invoice. All new invoices will automatically have the Project's Billing Address, going forward.
If it's not the Billing Address you mean please let us know so we can look further into it.