I have DNS-O-MATIC working with a cron job. Below are the steps:
1.- In web interface of Zeroshell go to Setup
2.- Click on Startup/Cron
3.- At the bottom of the pop up window click “add job”
4.- Give the job a name.
5.- In the main Text Area paste the following code (replace password and username accordingly):
6.- Select the time intervals for running the job.
7.- DNS-O-MATIC should now be updating. You are good to go!!