I guy I've met in Berlin receives a UBI independent from any government institutions.
He is truly disconnected from the system and for him it roughly worked like this.

The first 2-3 months he just enjoyed the UBI, it was summer and he enjoyed the stress free situation of not having bureaucrats pressuring him to find a job.
Then fall kicked in, and he got bored. He turned his free time into a little business, this business soon employed him fulltime, and he hired a person to help him.
During the spring the both of them rented a space and made enough money to fund half a UBI for someone else. So 1 UBI turned into 3 UBI and 2 fulltime jobs. So on top of the UBI they earned a decent amount of money that made it worth all the trouble.

I don't know what the status is right now, this was 2010 somewhere. And I've not been in Berlin since.

The UBI turned out to have a lot of value.

On the other hand I have seen a UBI 'experiment' under government control. With a couple of 'additional rules'. Those additional rules just made things complicated and out of fear for bureaucratic reprimands the participants in that experiment heasitated to do what they wanted to do. They did not dare to start a small business due to the additional rules that made it more expensive then what they could afford to do.
And guess what. Bureaucracy made the experiment fail. And the media blew the failure out of proportion. Saying UBI is impossible!

So UBI CAN work, and UBI CAN fail. It depends on many things. But if the ruling class does NOT WANT succes, then they just add rules.

Control is where it fails, the ruling class fears to loose control. And that's where their rules come around the corner.