With full access to your rest connection configuration, it is difficult to determine which items in you rest connection configuration that may need to be updated.
Also a 404 error connection failed could also mean that there is simply something blocking between your Sense server and the NPrinting server that you are attempting to connect to or even the account you are using in your rest connector is not valid or is not an administrative role on the NP server.
Make sure firewalls are not blocking the connection attempt, that the NP server and QS server are in the same domain and the user account in the connection is NP admin role member within the NP web console. (use the NP service account user id and credentials as your login credentials.
Rest connection Test fails usually if there is a syntax error in your rest connection, bad password or other invalid login information, mis-typed rest connector information such as an invalid url or an incorrectly configured NPrinting server possibly.
Also I suggest that you ensure that you are using April 2019 or later version of Qlik Sense which resolves a problem with the rest connector that resolve other issues unrelated to this post connection test failure.
Check the following Community Document for more information.
Please include the URL (also without the domain) in the screenshot so we can check if it is correct.
Best Regards, Ruggero --------------------------------------------- When applicable please mark the appropriate replies as CORRECT. This will help community members and Qlik Employees know which discussions have already been addressed and have a possible known solution. Please mark threads with a LIKE if the provided solution is helpful to the problem, but does not necessarily solve the indicated problem. You can mark multiple threads with LIKEs if you feel additional info is useful to others.