Hi rudolphmouton,

Thank you for your response. I would suggest contacting our Customer Support Team to further check and verify the email address of the user you're trying to add in a secure environment.

Here's how to contact us:

1. Sign in to your QuickBooks Online company.
2. Select Help (?).
3. In QB Assistant, enter the topic you need help with. You can also enter questions.
4. Select Contact Us to connect with a live support agent.
5. Choose a way to connect with us.

Feel free to post again if you have any other questions, we're here to help. Have a nice day!