In Moxie, each line item can be associated with projects, not entire invoices. The option to associate a "chunk" of the invoice to a project is at the line item level.

The intention is that you can have multiple projects represented in a single invoice.

If you've sent an invoice using "+ Add new line item" and your product and service library, you can still associate that line item to a project.

1) Return the invoice to draft status by clicking the 3 dots in the upper right of the invoice.

Note: Your client will not be notified of changes to invoices which allows you to do this. It also means if you make a change to the invoice, you'll need to re-send to your client to alert them of the change.

2) Click on the row and choose "Assign to project" to associate the line item with the project.

3) After you select the project, click "Mark as sent" option from the 3 dots in the upper right to return it to a "Sent" status.