feePaid property
The fee this split pays, in satoshis: the source minus the outputs of the signed transaction. Null when no transaction was built, and null is the honest answer there — a fee of zero would be an invention, not a measurement (bead libspiffy-q28i).
A fee here is what the transaction carries, not proof that it reached a miner: only isSuccess outcomes have been accepted or queued.
Implementation
final BigInt? feePaid;