I can't add a user. Just opens a blank screen.

Hello there, @mary90.

Thank you for posting here in the Community. I can help you add a user in QuickBooks Online.

First, please make sure you have permission to manage other users. Only an admin of the account can perform the invite process in the system.

To check your user type, please follow these steps:

1. Click the Gear icon in the upper-right corner.
2. Select Manage users.
3. Check the user type. 

If you're an admin and the blank screen persists, I suggest logging into your QBO account using a private browser. It's a great way to isolate browser-related issues.

If you're using Mozilla Firefox or Microsoft Edge, press the CTRL + Shift + P shortcut on your keyboard. For Safari, hit Command + Shift + N. Press CTRL + Shift + N if you're using Google Chrome. 

If it works, let's clear your browser's cache to access QuickBooks in a clean slate, so it'll function efficiently. If private browsing doesn't work, use other supported web engines to get the best and most secure experience.

For more information, as well as how to manage users in QuickBooks, I recommend the following article: User types and user permissions in QuickBooks Online.

Drop me a comment below if you have any other questions. I'll be happy to help you some more.