Complex sentence: The Federal Reserve Banks ("the Fed "), responsible for obtaining coins from the Mint and distributing them on request to member banks, also received coins banks did not need, a process known as"flowback".
Split into simpler sentences: The Federal Reserve Banks ("the Fed ") were responsible for obtaining coins from the Mint, and distributing them on request to member banks. Those banks returned coins not necessary for immediate needs to the Fed, a process known as"flowback".