In general in the MCU that's a suspense of disbelief type of issue - in the past they were working for SHEILD, then more directly with Stark. At this point they must be somewhat still working for/with the Government, since they ended up on the same mission as fake Cap, and they mentioned Redwing being "government property".

I would have assumed that they'd still have some Stark funding, or Fury funding, but since they specifically mentioned Sam's $$$ problems either that isn't the case, or any funding is specifically only for related expenses (like their flight to Europe) and maybe some compensation, but not enough for him to be helping to fund the family business (or even to show regular income for a business loan.)

All this being said, since they brought up the money issue, I'd assume that it will come up again at some point with some kind of explanation. Plenty of time to do that, and I always appreciate when a show doesn't lay everything out at once, but plants seeds that are then revisited later.