Hello,
That is the default return for that page if it does not return a file, it shows a 404. The url is valid.
So there is one more step. You have loaded the xml file, you need to now load the subscription data into it. To do this, go to awocoupon, delete your subscription and re-add it. This will load the subscription data into the update sites url.
Then go to extension > manage > update and clear cache before running the update again.