Send a Transaction While Paying the Fee with a Different Token¶
Introduction¶
The Asset Hub provides a powerful feature that allows users to pay transaction fees using alternative tokens instead of the native token of the chain.
This tutorial demonstrates how to send a DOT transfer transaction while paying the fees using a different token (USDT in this example) on the Asset Hub.
Environment Setup¶
Let's set up the development environment for this tutorial:
-
Create a new directory and initialize the project:
-
Initialize the project:
-
Install dev dependencies:
-
Install dependencies:
-
Create TypeScript configuration:
The command
npm pkg set type=moduleis used to set the type of the project to module. This is necessary to use theimportstatement in the TypeScript code. -
Generate Polkadot API types for Asset Hub:
-
Create a new file called
fee-payment-transaction.ts:
Local Asset Hub Setup¶
Before running the script, you'll need to fork the Asset Hub locally using Chopsticks:
This command forks the Asset Hub chain, making it available at ws://localhost:8000. By running polkadot-asset-hub, you're using the Asset Hub fork with the configuration specified in the polkadot-asset-hub.yml file. This configuration defines Alice's account with USDT assets. If you want to use a different chain, ensure the account you're using has the necessary assets.
Implementation¶
In the following sub-sections, you’ll set the stage with imports and a few constants, introduce the transaction signer, and connect to the Polkadot Asset Hub chain. Then you’ll craft a simple DOT transfer and send it, asking the network to charge the fee in USDT instead of DOT.
Import Dependencies¶
Add the following imports to your fee-payment-transaction.ts file:
import { sr25519CreateDerive } from "@polkadot-labs/hdkd";
import {
DEV_PHRASE,
entropyToMiniSecret,
mnemonicToEntropy,
} from "@polkadot-labs/hdkd-helpers";
import { getPolkadotSigner } from "polkadot-api/signer";
import { createClient } from "polkadot-api";
import { assetHub } from "@polkadot-api/descriptors";
import { withPolkadotSdkCompat } from "polkadot-api/polkadot-sdk-compat";
import { getWsProvider } from "polkadot-api/ws-provider/node";
import { MultiAddress } from "@polkadot-api/descriptors";
Define Constants¶
Define the constants for your transaction:
const TARGET_ADDRESS = "14E5nqKAp3oAJcmzgZhUD2RcptBeUBScxKHgJKU4HPNcKVf3"; // Bob's address
const TRANSFER_AMOUNT = 3_000_000_000n; // 3 DOT
const USD_ASSET_ID = 1337;
Create a Signer¶
Create a signer using Alice's development account:
const createSigner = async () => {
const entropy = mnemonicToEntropy(DEV_PHRASE);
const miniSecret = entropyToMiniSecret(entropy);
const derive = sr25519CreateDerive(miniSecret);
const hdkdKeyPair = derive("//Alice");
const polkadotSigner = getPolkadotSigner(
hdkdKeyPair.publicKey,
"Sr25519",
hdkdKeyPair.sign
);
return polkadotSigner;
};
This function will return a signer that can be used to sign the transaction.
Setup the Client and API¶
Create the client connection to the local Asset Hub:
const client = createClient(
withPolkadotSdkCompat(
getWsProvider("ws://localhost:8000") // Chopsticks Asset Hub
)
);
const api = client.getTypedApi(assetHub);
Create the Transaction¶
Create a standard DOT transfer transaction:
const tx = api.tx.Balances.transfer_keep_alive({
dest: MultiAddress.Id(TARGET_ADDRESS),
value: BigInt(TRANSFER_AMOUNT),
});
This creates a transaction that transfers 3 DOT to Bob's address while keeping Alice's account alive.
Sign and Submit with Alternative Fee Payment¶
The key part of this tutorial is specifying an alternative asset for fee payment. This is done through the asset parameter in the signAndSubmit options:
const signer = await createSigner();
const result = await tx.signAndSubmit(signer, {
asset: {
parents: 0,
interior: {
type: "X2",
value: [
{ type: "PalletInstance", value: 50 },
{ type: "GeneralIndex", value: BigInt(USD_ASSET_ID) },
],
},
},
});
const { txHash, ok, block, events } = result;
console.log(`Tx finalized: ${txHash} (ok=${ok})`);
console.log(`Block: #${block.number} ${block.hash} [tx index ${block.index}]`);
console.log("Events:");
for (const ev of events) {
const type = (ev as any).type ?? "unknown";
console.log(`- ${type}`);
}
process.exit(0);
This specifies that the fees should be paid using the USDT asset.
Full Code¶
The full code for the complete implementation is the following:
Complete Code
import { sr25519CreateDerive } from "@polkadot-labs/hdkd";
import {
DEV_PHRASE,
entropyToMiniSecret,
mnemonicToEntropy,
} from "@polkadot-labs/hdkd-helpers";
import { getPolkadotSigner } from "polkadot-api/signer";
import { createClient } from "polkadot-api";
import { assetHub } from "@polkadot-api/descriptors";
import { withPolkadotSdkCompat } from "polkadot-api/polkadot-sdk-compat";
import { getWsProvider } from "polkadot-api/ws-provider/node";
import { MultiAddress } from "@polkadot-api/descriptors";
const TARGET_ADDRESS = "14E5nqKAp3oAJcmzgZhUD2RcptBeUBScxKHgJKU4HPNcKVf3"; // Bob's address
const TRANSFER_AMOUNT = 3_000_000_000n; // 3 DOT
const USD_ASSET_ID = 1337;
const createSigner = async () => {
const entropy = mnemonicToEntropy(DEV_PHRASE);
const miniSecret = entropyToMiniSecret(entropy);
const derive = sr25519CreateDerive(miniSecret);
const hdkdKeyPair = derive("//Alice");
const polkadotSigner = getPolkadotSigner(
hdkdKeyPair.publicKey,
"Sr25519",
hdkdKeyPair.sign
);
return polkadotSigner;
};
const client = createClient(
withPolkadotSdkCompat(
getWsProvider("ws://localhost:8000") // Chopsticks Asset Hub
)
);
const api = client.getTypedApi(assetHub);
const tx = api.tx.Balances.transfer_keep_alive({
dest: MultiAddress.Id(TARGET_ADDRESS),
value: BigInt(TRANSFER_AMOUNT),
});
const signer = await createSigner();
const result = await tx.signAndSubmit(signer, {
asset: {
parents: 0,
interior: {
type: "X2",
value: [
{ type: "PalletInstance", value: 50 },
{ type: "GeneralIndex", value: BigInt(USD_ASSET_ID) },
],
},
},
});
const { txHash, ok, block, events } = result;
console.log(`Tx finalized: ${txHash} (ok=${ok})`);
console.log(`Block: #${block.number} ${block.hash} [tx index ${block.index}]`);
console.log("Events:");
for (const ev of events) {
const type = (ev as any).type ?? "unknown";
console.log(`- ${type}`);
}
process.exit(0);
Running the Script¶
To run the script:
Expected Output¶
When you run the script successfully, you should see output similar to:
Tx finalized: 0x771956fdf40b3741bdc3c1e981a6daacbe5521877ad1915542e7413bb4a820bc (ok=true) Block: #9645060 0x57710514f168b5c444c8e47b1e1a31dd9e7bc7e9a51d8d25ccdbc6053e159f6b [tx index 2] Events: - Assets - Balances - Assets - AssetConversion - Balances - Balances - AssetTxPayment - System
The key events to look for are:
- Assets: The asset was transferred.
- Balances: The fees were paid using the alternative asset.
- AssetConversion: The fees were converted to the alternative asset.
- AssetTxPayment: The fees were paid using the alternative asset.
- System: The transaction was successful.
Conclusion¶
Paying transaction fees with alternative tokens on Asset Hub provides significant flexibility for users and applications.
The key takeaway is understanding how to specify alternative assets using the XCM location format, which opens up possibilities for building applications that can operate entirely using specific token ecosystems while still leveraging the full power of the network.
| Created: October 3, 2025