The Differences Between UBI and Negative Income Tax

The negative income tax might disincentivize work on like the lower end. A UBI preserves what's called the marginal incentive to work, which is for the next dollar I earn, how much of that dollar do I get to keep? The UBI has this big looming question hanging over it of where does the money come from? And my belief is that a flat tax on income is really the only plausible way to do that.