Hello pbel,

This is not the experience we wanted to have for our customers. Since you've tried doing the troubleshooting steps provided above. For us to better assists you, I'd recommend reaching out to our Customer Care Team. That way, one of our support can further check the invoice and the project you wanted to link in a secure form.

1. Go to Help (?).
2. Select Contact Us.
3. Enter your concern, then select Let's talk.
4. Choose a way to connect with us:

• Start a chat with a support expert.
• Get a callback from the next available expert.

Also, you might want to check this article to learn more about how to Add existing invoices to QuickBooks Online Projects.

Post a comment if you need more help with QuickBooks Online. The Community is here to help you.