I'm trying to add an existing inv. to a project, but as soon as i change the customer to the project all my inv. data disappears and i'm then left with an empty invoice

I know a way to fix this, @alvin8.

Your browsing history can be the reason why your invoice information disappears. Let's perform some browser troubleshooting steps so we can add a project to your invoice.

To start with, let's begin by accessing your account in a new incognito or private window of your browser to check if the issue is related to your current browser or not. To do so:

• Google Chrome: Ctrl + Shift + N
• Mozilla Firefox: Ctrl + Shift + P
• Safari: Command + Option + P

Once completed, you can log back into your account and upload your logo. If you can do so without any issues, you can clear your browser's cache to optimize it. Also, your browser can start from scratch and improve your QuickBooks Online browsing experience.

However, if you still received the same error message, let's switch and use a new browser application. Then, log back into your account and your logo from th

I've added this article for your reference: Add existing invoices to QuickBooks Online Projects.

Feel free to visit this resource for future reference on recording invoice payments in QuickBooks Online: Record invoice payments in QuickBooks Online.

Don't hesitate to add any details below if you need further assistance with the project feature. I'm always here to help you.