If X is greater than Y then the remainder will turn up as negative capital at the Fed. By accounting identity.
The Fed has no legal authority to refuse a payment order from Treasury. The Fed just needs to account for the order and wait until Congress sorts itself out.
In other words there is no such thing as an empty chest and if Biden had any sense he would order the Fed to pay and then take it to court if the Fed refused.
Courts are used to interpreting conflicting instructions from Congress and the constitution.
Neutralise the weapon once and for all.