Hello @kabuzaid,
Welcome to this Forum. Hope we can help you.
First of all, have you checked this previous topic?:
Also, I would suggest to check our documentation:
https://docs.opennebula.io/6.6/management_and_operations/vm_management/vm_instances.html
And if possible, paste the error (if persists), to check where could be the origin of the problem.
Regards,