How can I get access to my client's data? He sent me an invite using the email but I am not able to see his data.

Thanks for sharing your concerns, @cmuswere-gmail-c. After you accept the client's invitation, that'll show you the list of all your clients. Check this article for more insights: How to access a client's company in QuickBooks Online Accountant. 

Since you're unable to see your client's data, it could be that the piled-up cache in your regular browser caused this unusual behavior. I'd suggest using a private browser when switching from one client to another: 

• For Chrome, press Ctrl + Shift + N.
• For Internet Explorer or Firefox, press Ctrl + Shift + P.
• For Safari, hold down Command + Shift + N.

If it works, proceed and clear the cache on your regular browser. If it's not, use another supported, up-to-date browser. 

For future reference, read through this article to learn more about opening and reviewing clients' QuickBooks Online account. It also covers links to a different topic that can help you in opening your client's QuickBooks account. 

Let us know if you need further help with anything else. We're always here to assist. Have a wonderful day!