Signable Data
A SignableData object is the packet actually signed. It works as a wrapper over transaction id and signature metadata. Note that when multi-transaction signing (signing a block of transactions) is used, the root of the Merkle tree (having transaction IDs as leaves) is actually signed and thus txId refers to this root and not a specific transaction.
Parameters
tx Id
transaction's id or root of multi-transaction Merkle tree in case of multi-transaction signing.
signature Metadata
meta data required.