Some people have more money than they need, it can be removed from them - the intricacies of how they got that money should be very carefully considered when it comes to structuring how UBI would be funded - but they clearly have more money in absolute terms. And that wealth is transferable.
Also, in the western world, we have enough of everything. No one starves in America because there isn't enough corn, they starve because they don't have enough money to afford it - no one is homeless because no homes could be built, they're homeless because nobody wants to pay for the home to be built.
These are all solvable problems.