g920t Initializating zTool… error (0)

hi guys, im having an problem trying to unlock a g920t 5.1.1 , on version OJ7
the problem is that every time i try to unlock i get that error message
Initializating zTool… error (0)
Done with Samsung Tool PRO v.24.4

is there any solution to it, i wonder if i can downgrade without bricking the phone, but wanted to ask before i act on it, if any one can help please and thank you