portusctl does not implement all the API entrypoints available as of Portus v2.4. You can follow the progress of this here. The exec command is considered stable already, and that's why portusctl is included inside of the Portus Docker image as of v2.4. Note well: portusctl is targetting the API from the Portus' master branch, which is still under heavy development. Hence, we recommend using both the latest portusctl together with the latest commit of Portus. This situation will change once the API starts to stabilize.