The simulated withdrawal callback exercises applyPayoutOutcome's three branches (full / partial / zero-delivery reversal) against the real ledger through the real inbound webhook path.
The callback is signed by OUR OWN implementation of MyPays24's documented signature scheme and verified by that same implementation. It does not prove MyPays24's real signature scheme matches ours, and it does not resolve whether their fee_type is merchant or customer. Both still require live provider traffic.