This might help.
Once you have installed the device handler do the following to add the device to ST.
Login to ST IDE.
Click "My Devices"
Click "+ New Device", top right corner.
Fill out the information. For "Device Network ID" give it a unique id. I do something like my initials with a long sequential number. Maybe "PTC000001" in your case. If you create another device increment the number, "PTC000002".
Don't select a group or enter a zigbee ID.
Once you have done this, the device will appear in your ST app.
Find the device in the ST app.
Once in the device, click the configure button (cog).
Take a look at the settings options.
There are two critical fields. "Bulb Name" and API Token.
The bulb name should be exact (case-sensitive) to what it is called in LIFX.
Follow the instructions here to get your API token.