Doubt about the mag identifier

In an emulator generate

mag-identifier: UmV0b1VTeTJZeWx6bE15bXJzRTE0VklYakJRPQ ==

My doubt is that there is some way to correctly generate that mag because when I randomly generate letters and numbers I get this error

The given mag-identifier is either invalid or points to an unknown device

You cannot generate it randomly because you do not know that it is encrypted. because that cade is an encryption that includes bs64 and you need to know what it is encrypting so that in that way you generate it randomly and encrypt it so that you do not have that error

I understand thanks for answering