In order to test whether there are any network issues, go to your browser and enter the following URL:
http://[IP address of tablet device]:53652/check
You should get a result with the device type and the Twixl Viewer version number like:
ipad-retina|4.2.6 / android10|4.2.6 / phone_m|4.2.6
If a soft- or hardware firewall is active on your network, and you seem to be unable to send a preview to a device, make sure to ask the network administrator to open TCP ports 53652 & 53653.