User B is sending a peer-to-peer transaction, akin to a Zelle or Venmo. In most other countries, these peer-to-peer payments (PIX, UPI, etc.) do billions of transactions per month. And since you're sending your own funds, you're not a money transmitter. If we do work with any larger entities (e.g., an OTC desk, liquidity provider), we'd certainly be cognizant of the relevant licensing.
Do you check the laws for this in each country you are available in?
Do you notify user B of this fact and the potential legal risks?
Do you verify if they have the license?