A colleague cannot join qbo, and keeps getting the message "invalid link". how do i fix this?

Thanks for checking the error on your end, @prith. I can see there are specific cases or ongoing investigations about the issues you're having with adding users to QuickBooks Online. Let me help you how to fix this.

I can see the challenges and the urgency of resolving them. Our engineering team doubles their time to settle the error about the invalid link on inviting users. Furthermore, it would be best to contact our support team. This way, they can add you to the involved users. 

Here's how:

1. Log in to your account.
2. Click the Help button at the top right corner.
3. Go to the Search tab, then select Contact Us.
4. Enter a brief discussion with your concern, then click Continue.
5. Choose to Have us call you to connect with us.

For your convenience, here are the support hours for different QuickBooks Online plans:

Plus, Essentials, Simple Start:

• Monday to Friday: 6 AM to 6 PM PT
• Saturday: 6 AM to 3 PM PT

Advanced:

• Support is available anytime, any day.

Following the steps above will allow you to receive updates on the available fix. My purpose is to provide information and assist with answering questions to the best of my abilities. If you have any specific questions or need assistance with a particular topic, feel free to ask, and I'll do my best to help you.