Based on the questions and answers from support on the site that you linked to, that model will only work with a control4 system, which uses a proprietary Zigbee profile that is not the same as the one used by smartthings.
The Zigbee lock is only used with a Control 4 home automation system.
I would suggest contacting their support in case something has changed, since those posts were about two years old. But it might not be compatible. 
I should also add that 40 to 50 feet away is near the maximum distance for a Zigbee device, so it could also just be a range issue. If it is compatible with smart things, you might need to add another mains-powered Zigbee device like a plug-in smart plug about halfway between the lock and the hub. Zigbee is a very low power protocol, which means that batteries last a long time, but it also means transmissions don’t go very far.
See post 11 in the following community FAQ, then go up to the top and read the whole thread to learn more about range. The topic title is a clickable link.