We have state and local governments for a reason. Something as risky and expensive as UBI, if it is going to be implemented, should be implemented gradually with proper testing, feedback, and adaptation.
Just consider the simplest thought experiment: levy a one-off extra tax of $0.01 on every tax payer and credit some random poor person. This is almost certainly a strict Pareto improvement, but it clearly doesn't scale.
In the U.S., this already happened in Alaska with the Alaska Permanent Fund. All residents of Alaska receive annually a portion of the proceeds from Alaska's oil revenue. Alaska tried to prevent internal migrants from receiving this by having the dividend be dependent on a person's years of residency in Alaska , but this was struck down by the U.S. Supreme Court in Zobel v. Williams[2]. Now, anyone who has lived a whole year in Alaska is eligible to receive the dividend.
As such, a social safety net as generous as UBI will likely not be workable in the United States. Other states' unemployed residents would likely swarm the state with UBI. (Unless of course, if the Supreme Courts decides to reverse its decision in Zobel v. Williams.)
[1] https://en.wikipedia.org/wiki/Alaska_Permanent_Fund#Permanen...
[2] https://supreme.justia.com/cases/federal/us/457/55/
"Under the plan, each adult resident receives one dividend unit for each year of residency subsequent to 1959, the first year of Alaska's statehood. Appellants, residents of Alaska since 1978, brought an action in an Alaska state court challenging the statutory dividend distribution plan as violative of, inter alia, their right to equal protection guarantees. ... the dividend statute creates fixed, permanent distinctions between an ever-increasing number of classes of concededly bona fide residents based on how long they have lived in the State."
Most countries which are not the Unites States don't have the power to make large scale systematic changes that this requires. It might not be possible even in the US, what with states shipping homeless people to other states and all.