Sponsored Transactions

const tx = new Transaction();

// ... add some transactions...

const kindBytes = await tx.build({ provider, onlyTransactionKind: true });

// construct a sponsored transaction from the kind bytes
const sponsoredtx = Transaction.fromKind(kindBytes);

// you can now set the sponsored transaction data that is required
sponsoredtx.setSender(sender);
sponsoredtx.setGasOwner(sponsor);
sponsoredtx.setGasPayment(sponsorCoins);