I spent some time troubleshooting some basic problems setting up PTM today. There are a few items that may not be called out all that well in the documentation that can trip you up quite easily.
Hostname is rather important. This may be obvious to some, but news to others. Make sure that /etc/hosts and /etc/hostname both reflect the name you use in the topology.dot file. If not, you'll likely get an error when attempting to start the ptmd process.
Editing the topology.dot file. There is a really easy way to ensure the file format is correct. Simply open the file with Graphviz to ensure its readable. If you edit topology.dot file from a Windows machine, be sure to double check file formatting... you may have extra characters that you aren't aware of that keep the graph from working correctly.
PTM is one of my favorite Cumulus Linux features. It's not difficult to setup or use yet provides a lot of value. Don't let these two easily overlooked items trip you up.