Locks Management RBACK Role not appears in some subscriptions.

Hi to all,

i need to solve my question about RBACK permissions in azure subscriptions. 

i have the subscription A. when i want to assign locks management role to a user it apears with no problem.

I have the subscription B. when i want o assign the same rol "Locks management"  this is not listed in the role  list for assigment.



Thanks

Best Regards