@tbs86 - At first glance, it looks like Maven is having trouble locating the defined target. Maven works by defining configurations to assist with compilation. “Exec”, “test”, “debug”, “production”, etc. are all examples of Maven targets. At first blush, it seems that the Maven XML file does not include a target named “exec”.
I don’t think you’re doing anything wrong, per se. More likely, someone has updated the Maven file and the instructions are out of date.