Why not? You could use it to lower the cost of your services. (Someone is obviously earning interest on it. Better you than your bank.)
In the U.S., I don’t think money transmitters are allowed to do this. (They can keep the interest earned on it.)
Financing from deposits is more a crypto thing.
They are literally funding themselves out of deposits, in a small way if they keep any persons money for any period of time. If they start doing it to lots of people for months at a time then they are at least partially funding themselves from their customers.
Lots of businesses do this incidentally. A good one is businesses selling gift cards. It's not the same; but this set of conditions is not super uncommon.
No, they probably are not. It’s illegal and money transmitters are regulated.
What they are doing is collecting interest. One tends to see less scrupulous transmitters hold funds longer when rates rise. I didn’t think Stripe fell in this category, but it’s becoming difficult to say.
> good one is business selling gift cards
You’re right. (Also customer deposits.) This doesn’t apply to money transmitters, however.
If they hold a bunch of cash from people it is effectively theirs for that period of time. This could prevent them from needing to raise a funding round if done enough.
Some businesses are literally customer funded like these.
If you want to read more search for "negative cash operating cycle".