Hey everyone,
This thread has multiple issues going on that may not be related. I do have a couple general ideas that can help both of the main issues going on though so everyone can get the Battle.net application installed and get back to their gaming.
For anyone who is receiving the Failed - Network Error when downloading the installation file for their game or the Battle.net application, please see if the alternative links for directly downloading that file work. Our forum post here has it for each region. If one region does not work, test if another one does: [Main Thread] "Failed - Network Error" with Battle.net Set-up file
For everyone else, and also for those that try the above but still run into a problem, a lot of times download issues happen due to a network or ISP issue. A good way to rule such a problem is changing the network that you’re connected to. Please try an alternative connection or even a phone hotspot/tether. Usually this is just needed to get around corrupted data and you can switch back to your normal network after the installation is done. If everything is found to work only on the alternative connection though, then talking to your ISP would be advised.
If this doesn’t help out, please create a new separate post with some additional information such as errors seen and troubleshooting already done and we can share some more personalized steps.