Signing a Tron transaction is identical to how we sign an Ethereum or Solana transaction with the exception that we need to pass in the Tron specific RPC URL, chain ID, and method.
You can get an RPC URL for Tron from www.trongrid.io.
In the example we are going to update:
  • chainID to tron:nile
  • rpcUrl to grpc.nile.trongrid.io:50051?api_key=<API_KEY>
  • method to tron_sendTransaction
  • params to a base64 encoded serialized Tron transaction
Here is a short snippet of how to get the params using tronweb, for a complete example checkout this example repo: 
const tnw = require('tronweb');

const tronWeb = new tnw.TronWeb({
    fullHost: 'https://nile.trongrid.io',
    headers: { 'TRON-PRO-API-KEY': 'API_KEY' },
  });
  const fromTronHexAddress = tronWeb.address.toHex("YOUR_TRON_ADDRESS");
  const toHexAddress = 'RECIPIENT_ADDRESS';
  const builtTx = new tnw.TransactionBuilder(tronWeb);


  const transaction = await builtTx.sendTrx(
    toHexAddress,
    1,
    fromTronHexAddress,
  );

  // // Serialize the transaction
  const txPb = tronWeb.utils.transaction.txJsonToPb(transaction)
  const rawData = txPb.getRawData().serializeBinary();

  // // Base64 encode the serialized transaction
  const base64Transaction = Buffer.from(rawData).toString('base64');

  // Sign the transaction
  const signResponse = await axios.post(
    `${PORTAL_MPC_CLIENT_URL}/v1/sign`,
    {
      share: shares.SECP256K1.share,
      method: 'tron_sendTransaction',
      rpcUrl,
      params: base64Transaction,
      chainId: 'tron:nile',
    },
    {
      headers: { Authorization: `Bearer ${clientApiKey}` },
    },
  );
Below is an example curl command for signing a Tron message: 
curl -X POST 'https://mpc-client.portalhq.io/v1/sign' \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer <clientApiKey>' \
  -d '{
    "share": "SECP256K1.share",
    "method": "tron_sendTransaction",
    "params": "BASE64_ENCODED_TRANSACTION",
    "rpcUrl": "YOUR_RPC_URL",
    "chainId": "tron:nile"
  }'
The RPC URL for Tron uses the GRPC protocol, not HTTP.

​
Supported Methods and ChainIds

Methods:
  • tron_sendTransaction
ChainIds:
  • tron:mainnet
  • tron:nile
  • tron:shasta