Virtual machine is not listed with
prlctl list -a command even after you register it using
prlctl register command.
Register command is showing that VM is successfully registered and if you are trying to register it at second time it shows that it is already registered:
# prlctl register VM.pvm Register the VM... Failed to register the VM: The virtual machine "VM" is already registered. You cannot register a virtual machine more than once.
You are trying to register VM template but not VM.
Check if your template is available using
prlctl list -t command, if yes - it is registered already.