Your streaming provider can sometimes close a connection if they are not receiving data consistently. Below is an outline of a few issues that could contribute to getting a "connection closed by server" error:
The Upload bandwidth from your Internet Service Provider (ISP) can sometimes fluctuate. Try lowering your video bitrate (i.e. make sure it doesn't exceed available upload bandwidth. You can use speedtest.net to check your connection, or you can download the Speed test app on your main switching device). You can lower the bitrate within the Outputs tab by adjusting the parameters for your channel.
Make sure that your video's resolution matches the settings selected on your streaming provider's account. If the streaming video service expects 640x360 video, then you need to make sure that you are sending out video at 640x360, and not something like 1280x720. This can also be adjusted through the channel parameters.
Make sure that you have a strong WiFi connection (check the WiFi icon at top of the device being used as the Switcher). If you have a weak WiFi connection, then Switcher Studio cannot properly send information, and your streaming video provider may timeout the connection.
Make sure port 1935 is open, and check required networking specs.
If you continue having issues, please contact your Internet Service Provider.