I already set my client as primary admin, but why they still cannot see the invoices?

Hi info1508,

Welcome to the Community. It's vital your client is able to see the invoices as the primary admin on the account. I'll be glad to steer you in the right direction so you can get back to managing your work with peace of mind. 

Based on the details you've shared above, I suspect you may be experiencing a browser-related issue that's causing the issue. Clearing cache and cookies helps with fixing most browser issues. You can do this by following the steps in this article: Clear Cache and Cookies. I encourage you to give this a try on your browser when you get a chance. 

Feel free to let me know what happens. I'll be here in case you have other questions.