// ABI for transaction extension, required for serialize transaction
"version": "eosio::abi/1.0",
let buffer = new Serialize.SerialBuffer({ textEncoder: new TextEncoder(), textDecoder: new TextDecoder() });
const sponsorType = Serialize.getTypesFromAbi(api.abiTypes, ext_abi).get('sponsor_ext');
sponsorType.serialize(buffer, {"sponsor": "<SPONSOR_ACCOUNT_NAME>"});
transaction_extensions: [{
data: Serialize.arrayToHex(buffer.asUint8Array())
// TODO send trx TO sponsor