Android: "Bad Request-Invalid Hostname" When accessing localhost from emulators

Open your solution folder. You might have several projects inside 1 folder, you don't need project's folder but the root one. Inside you'd have .vs/config/applicationhost.config file, open it.

find <sites> inside you'll have sites that you are running, might have several, if you switch startup projects in one solution. The name will be corresponding to one displayed by IIS in taskbar when you right-click it's icon. The tag could be, for example, <site name="ServerApp" id="2">. Now you need to add a line to bind external connections to your machine ip, for example

      <site name="ServerApp" id="2">
...
        <bindings>
...
          <binding protocol="http" bindingInformation="*:60424:127.0.0.1" />
        </bindings>
      </site>

Set appropriate port number and protocol, what matters here is just map them to 127.0.0.1, not "localhost" then they will be available for android emulator via 10.0.2.2:60424 (the port number 60424 is just from the example above, use yours)

You can use our free extension Conveyor https://marketplace.visualstudio.com/items?itemName=vs-publisher-1448185.ConveyorbyKeyoti

If the IP that Conveyor gives you doesn't work, just substitute it with 10.0.2.2. Using Conveyor solves the problem of needing to make IIS Express bind to other hostnames. It also has some other features too.