Usb or serial print not detecting port

Hi All ,

i want to print through usb or serial ,but i am not able to discover the port using starPRNT plugin. that giving always empty response , whereas at the same time other apps to print and detect everything. i am not getting how to use serial ,because how we will get vid and PID of device .there is no such method in serial .how the requestPermission() method will ,if we don’t have the device details .
whenever i am trying to requestPermission() method .it’s giving me “No Device Found” error .

please help asap.

Any help will be appreciated.

Subodh kumar Rai