From what I can tell as a lay observer, such schemes are likely illegal in the US. Excepting certain entities with specific legal carveouts or very careful navi

From what I can tell as a lay observer, such schemes are likely illegal in the US. Excepting certain entities with specific legal carveouts or very careful navigation of the legal system such as Paypal and Venmo, every scheme that I am aware of in the US is just maintaining an account with a single provider that you charge and draw down for services from that single provider (e.g. Walmart could allow you to make a Walmart account that you can use to pay for goods from Walmart). Circumstantial evidence leads me to believe that the two key aspects that are illegal are: withdrawal (recovering your balance into a fungible form) and 3rd party payment (account is managed by a different legal entity than the entity being paid) with the latter being the more impactful of the two. The reason the lack of 3rd party payment is deeply problematic is that without 3rd party payment the account must be associated with the ultimate provider of the goods/services, so the consumer can not consolidate or rebalance their funds. Therefore, it is highly undesirable for a consumer to maintain a rolling balance which is the only reason for such a scheme in the first place. As secondary evidence for it being illegal in the US, the scheme you are proposing is pretty much exactly what WeChat and Alipay do in China. It is also exactly the problem that Paypal and Venmo were made to solve, but for some reason they chose much more convoluted and restricted solutions even though from a technical standpoint it is harder to do what they actually did rather than the absolutely trivial technical problem of the fully featured solution which just manages account balances and transfers between them, a literal CS 101 type of technical problem.