Basic income means negative tax and it only makes sense if massive wealth inequality is addressed as well. Otherwise, it would fall prey to inflation. Wealth distribution is essential in any system with unfair outcomes and the neoliberal bullshit we are trapped in provides opportunity to only the wealthiest class, and a few lucky professionals. It is maximally unfair and therefore we need many fixes, basic income being only one of those fixes.
Yes, UBI is essentially a fully refundable tax credit. For someone paying more in taxes than the amount of UBI, the UBI lowers their tax burden. So if the UBI is $12,000 and someone owes $14,000 in taxes, then their taxes effectively go down $12,000 and they owe $2,000 instead of $14,000.
Of course, there will be those who taxes are increased beyond the size of the UBI in order to make the UBI possible, but they are mostly in the top 10% and their taxes will increase by around 10%. Those are the same people who are the only one benefiting from productivity increases for decades now, while the bottom 80% have received a smaller and smaller share of GDP decade after decade.
UBI is a mechanism for distributing productivity increases in a world where wages and salaries are no longer doing that thanks to increasing automation and falling collective bargaining power.
As for inflation concerns, yes, UBI is a tax and transfer policy, not a monetary expansion policy. There are some who would prefer monetary expansion to pay for it without tax increases, including billionaires like Bill Gross, but those voices are in the minority. The overwhelming majority of UBI proponents, myself included, believe it makes sense to raise taxes at the top, because they are the ones who own the machines who are replacing people in labor markets.
The way I would raise taxes however is not on income, but via other methods like consumption taxes, carbon taxes, land value taxes, and financial transaction taxes. I also like the idea of applying the Alaska Model to fund UBI with fees and royalties before the fact instead of taxation after the fact.
I also agree that UBI does not solve every problem, but I firmly believe (based on a continually growing amount of empirical evidence) that it's the precondition for solving a great many otherwise unsolvable problems, especially technological unemployment - which is very very real.