Hello Wismatix,

The error 404 means that the web page you're trying to reach could not be found on the server. Let's run some basic troubleshooting steps to isolate the problem. We can start with checking if your computer is connected to internet, and accessing QuickBooks Online in a private browser. This usually resolves any browser-related issues. 

Here's how to open a private browser:

•     Google Chrome: press Ctrl + Shift + N
•     Mozilla Firefox: press Ctrl + Shift + P
•     Internet Explorer: press Ctrl + Shift + P
•     Safari: press Command + Shift + N

Once logged in, please click on the Gear icon and choose Account and Settings. In the Payments section, click on Learn More. You'll be routed to the sign up page for our QuickBooks Payments. 

If you have any questions, please let us know. We'll be right here to help.