This doesn't make any sense.

For money to work it has to represent some real value, something that has some scarcity to it such as potatoes or hours of human labor. Ultimately it is just a decoupler in a barter system, a universally recognized IOU.

Why would someone give me a car in exchange for UBI-scrip when that UBI-scrip has no inherent scarcity or value and can be produced in infinite supply by the government ?