UBI is implemented tomorrow. Every citizen gets $1000 per month.
Landlord now knows you have an extra $1000 that you never had before. Why wouldn’t the landlord raise prices?
Now you have an extra $1000 a month and instead of eating rice and beans for a few meals you go out to a restaurant. The restaurant owners know everyone is eating out more so why not raise prices and maximize shareholder profit as always. The restaurant/corporation is on TV saying, “well, demand increased and it is a simple Economic principle that prices had to increase. There’s nothing we can do about it”.
Your state/country has toll roads. The state needs money for its deficit. UBI is implemented and the state/country sees it as the perfect time to incrementally raise toll prices.
Next thing you know UBI is effectively gone because everything costs more and billionaires keep hitting higher and higher all time net worth records.
People are focusing too much on your number, and too little on your take.
I think that a strong progressive tax works better than just two brackets (no taxation vs. full taxation). Specially when coupled with universal basic income - the idea is to eat the rich, not the slightly less poorer, on those you just nibble.