You’re in the right direction for help, @userjeremiahsemuyaba.

Let’s sort out your concern about error 404 in QuickBooks Online (QBO).

A stored cache can usually cause this error message when accessing any pages that include the clients' page. We can rule this out by using a private window or incognito:

• Google Chrome: Press CTRL + Shift + N.
• Safari: Press Command + Shift + N.
• Mozilla Firefox: Press CTRL + Shift + P.

Check the page after logging into your QuickBooks Online account. Manage your clients once the page load correctly. Clear the cache in the default browser to solve the problem altogether.

Close any open browser windows after the prompts are finished to complete the procedure. This will update your browser's cache with new, accurate information.

Since they don't use the data from the already-existing webpage, you can also use another supported browser.

Furthermore, refer to this article on how you can access your clients' accounting data, review their books, edit transactions, and fix issues: Open and review clients' QuickBooks Online or Self-Employed accounts

Afterward, you can check out this article to categorise and match online bank transactions and reconcile their account.

Should you have other concerns about accessing clients, you can always post them here. Have a good one!