Looking at such payments as being about fixing present problems rather than punishing living people for the sins of the dead, I don't have any problem with it. Governments should invest money in fixing problems and bringing as much fairness to the people's lives as is feasible. Apparently, that word starts with an F, not a PH. Weird.
But in some cases, I just don't see a way to make it work.
The USA could pay a native tribal council because that's another government, which can be treated as a single whole unit. The question of how much to pay could be debated & settled in fairly straightforward terms of what that whole tribe's problems and needs are, and it would be up to the tribal government to decide what to do with the money. Also, a tribal economy is pretty small compared to the USA's, so the expense to the USA would not be very significant.
With Japanese imprisonment in WWII, there was no such separate government to go through, but handling it on an individual scale would have been pretty straightforward because it was still exactly the same individuals who'd been mistreated in the first place, we had their identities, and they'd all had the same thing done to them. And again, there weren't too many of them (and the harm done to them had been smaller than in other cases we might compare theirs with), so the expense wasn't too vast.
None of that is true for black Americans, or for American descendants of slaves to American/Confederate owners, or for whatever other such group definition you could come up with (any one of which would include some people whom another definition excludes). They're a large enough fraction of the population that the financial burden would be dire. Worse yet, they don't have their own government for the USA's to interact with, either to discuss the appropriate payment amount with or to actually deliver the payment(s) to. So then we're stuck with paying individuals or maybe households, but on that scale, there's no way to determine who gets paid and who doesn't, or how much; there's just too much variation in every parameter you could imagine trying to use.