I have a project set up. I have income coming from another company that I invoiced, but is linked to the same project. How do I add that to the same project?

Hello Elizabeth, thanks for clarifying. What you can do is go to the invoice and adjust the name to be the project name and then receive payment on it, however that would move the customer transaction to be under a new name under the new project. If you want to keep the original invoice as is but make the income show against the project  the best way would be to go to the invoice itself and go to receive payment and then instead of receiving payment to the bank receive payment to the undeposited fund's chart of account and then save and close the invoice. Once that is done go to the +new symbol on the top right of QB and select bank deposit>put a tick in the payment and then in add funds to this deposit in the payee select the project name>in the account on the next line the income account and save and close( you will see the date and bank account in the very top right if you need to change those. If you then click in the project section you will see the payment, the invoice will show as paid as well.