I see 404 , and yes I have turned on the managed billing from shopify partner dashboard. Its kinda disappointing sometimes how bad some of the docs are or maybe the managed app billing service is down
Have you tried some troubleshooting steps such as switching to a different browser, use a different device, and clear your cookies and cache? If yes, and the issue still persists, I highly suggest that you reach out to Shopify support team so, they can further check your account and is what is causing this issue.
@tanmaykejriwal How did you turn on managed pricing from shopify partner dashboard? Do you mean just choosing the managed pricing option for the app or there is any other setting to be turn on after defining the managed pricing plans for the app ?