Hosted Deposit and Withdrawal

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This guide is available on three different programming languages: Typescript, Kotlin and Flutter (Dart). You can change the shown version on each page via the buttons above.

The SEP-24 standard defines the standard way for anchors and wallets to interact on behalf of users. Wallets use this standard to facilitate exchanges between on-chain assets (such as stablecoins) and off-chain assets (such as fiat, or other network assets such as BTC).

During the flow, a wallet makes several requests to the anchor, and finally receives an interactive URL to open in iframe. This URL is used by the user to provide an input (such as KYC) directly to the anchor. Finally, the wallet can fetch transaction information using query endpoints.

Get Anchor Information

Let's start with getting an instance of Interactive class, responsible for all SEP-24 interactions:

TypeScript

let sep24 = await anchor.sep24();

First, let's get the information about the anchor's support for SEP-24. This request doesn't require authentication, and will return generic info, such as supported currencies, and features supported by the anchor. You can get a full list of returned fields in the SEP-24 specification.

TypeScript

const getAnchorServices = async (): Promise<AnchorServiceInfo> => {
  return await anchor.getServicesInfo();
};

Interactive Flows

Before getting started, make sure you have connected to the anchor and received an authentication token, as described in the Stellar Authentication wallet guide. We will use the token object in the examples below as the SEP-10 authentication token, obtained earlier.

To initiate an operation, we need to know an asset. You may want to hard-code it, or get it dynamically from the anchor's info file, like shown above (for USDC):

TypeScript

const asset = info.currencies.find(({ code }) => code === "USDC").assetId;

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Before starting with the deposit flow, make sure that the user account has established a trustline for the asset you are working with.

Basic Flow

Let's start with a basic deposit:

TypeScript

let deposit = await anchor.sep24().deposit({
  assetCode,
  authToken,
});

As a result, you will get an interactive response from the anchor.

Open the received URL in an iframe and deposit the transaction ID for future reference:

TypeScript

let url = deposit.url;
let id = deposit.id;

Similarly to the deposit flow, a basic withdrawal flow has the same method signature and repose type:

TypeScript

let withdrawal = await anchor.sep24().withdraw({
  assetCode,
  authToken,
});
let url = withdrawal.url;
let id = withdrawal.id;

Providing KYC Info

To improve the user experience, the SEP-24 standard supports passing user KYC to the anchor via SEP-9. In turn, the anchor will pre-fill this information in the interactive popup.

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While SEP-9 supports passing binary data, the current version of the SDK doesn't offer such functionality.

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At the time, accepted SEP-9 is not strictly typed yet. Improved typing will be offered in future versions.

TypeScript

let deposit = await anchor.sep24().deposit({
  assetCode,
  authToken,
  extraFields: { email_address: "[email protected]" },
});

Changing Stellar Transfer Account

By default, the Stellar transfer will be sent to the authenticated account (with a memo) that initiated the deposit.

While in most cases it's acceptable, some wallets may split their accounts. To do so, pass additional account (and optionally a memo):

TypeScript

import { Memo, MemoText } from "stellar-sdk";

const recipientAccount = "G...";
const depositDifferentAccount = async (): Promise<InteractiveFlowResponse> => {
  return anchor.sep24().deposit({
    destinationAccount: recipientAccount,
    destinationMemo: new Memo(MemoText, "some memo"),
    assetCode,
    authToken,
  });
};

Similarly, for a withdrawal, the origin account of the Stellar transaction could be changed:

TypeScript

const originAccount = "G...";
const withdrawal = await anchor.sep24().withdraw({
  withdrawalAccount: originAccount,
  assetCode,
  authToken,
});

Getting Transaction Info

On the typical flow, the wallet would get transaction data to notify users about status updates. This is done via the SEP-24 GET /transaction and GET /transactions endpoint.

Alternatively, some anchors support webhooks for notifications. Note that this feature is not widely adopted yet.

Tracking Transaction

Let's look into how to use the wallet SDK to track transaction status changes. We will use Watcher class for this purpose. First, let's initialize watcher and start tracking a transaction.

TypeScript

let watcher = anchor.sep24().watcher();

let { stop, refresh } = watcher.watchOneTransaction({
  authToken,
  assetCode,
  id: successfulTransaction.id,
  onMessage,
  onSuccess,
  onError,
});

Alternatively, we can track multiple transactions for the same asset.

TypeScript

let watcher = anchor.sep24().watcher();

let { stop, refresh } = watcher.watchAllTransactions({
  authToken,
  assetCode,
  onMessage,
  onError,
});

Fetching Transaction

While Watcher class offers powerful tracking capabilities, sometimes it's required to just fetch a transaction (or transactions) once. The Anchor class allows you to fetch a transaction by ID, Stellar transaction ID, or external transaction ID:

TypeScript

const transaction = await anchor.sep24().getTransactionBy({
  authToken,
  id: transactionId,
});

It's also possible to fetch transaction by the asset

TypeScript

const transactions = await anchor.sep24().getTransactionsForAsset({
  authToken,
  assetCode,
});

Submitting Withdrawal Transfer

Previously, we took a look at starting the withdrawal flow. Now, let's take a look at a full example.

First, start the withdrawal:

TypeScript

let withdrawal = await anchor.sep24().withdraw({
  assetCode,
  authToken,
});

Next, open an interactive url :

TypeScript

let url = withdrawal.url;
// open the url

After that we need to wait until the anchor is ready to receive funds. To do so, we will be waiting until transaction reaches pending_user_transfer_start status

TypeScript

let watcher = anchor.sep24().watcher();

let onMessage = (transaction) => {
  if (transaction.status === "pending_user_transfer_start") {
    // begin transfer code
  }
};

let { refresh, stop } = watcher.watchOneTransaction({
  authToken,
  assetCode,
  id: successfulTransaction.id,
  onMessage,
  onSuccess,
  onError,
});

Next, sign and submit the Stellar transfer:

TypeScript

const txBuilder = await stellar.transaction({
  sourceAddress: keypair,
  baseFee: 100,
});

const transfer = txBuilder
  .transferWithdrawalTransaction(walletTransaction, asset)
  .build();

keypair.sign(transfer);
stellar.submitTransaction(transfer);

Where keypair is the SEP-10 authenticated account. If you want to transfer funds from a different address, refer to Changing Stellar Transfer Account section.

Finally, let's track transaction status updates. In this example we simply check if the transaction has been completed:

TypeScript

let watcher = anchor.sep24().watcher();

let onSuccess = (transaction) => {
  // transaction came back as completed / refunded / expired
  console.log("Transaction is completed");
};

let onError = (transaction) => {
  // runtime error, or the transaction comes back as
  // no_market / too_small / too_large / error
};

let { refresh, stop } = watcher.watchOneTransaction({
  authToken,
  assetCode,
  id: successfulTransaction.id,
  onMessage,
  onSuccess,
  onError,
});