Bridge with Privy Server Wallets

Bridge ERC-20 tokens through Layerswap from a Privy server wallet using gas sponsorship

This flow bridges ERC-20 tokens through Layerswap using a Privy server wallet. It creates a swap with use_depository: true, batches the token approval with the bridge call, and submits everything through Privy’s gas sponsorship — so the wallet doesn’t need native tokens for gas. See the full example on GitHub.

Prerequisites

• A Layerswap API key
• A Privy app with server wallets and gas sponsorship enabled
• Source-token funds on the Privy wallet address

Testnets are supported — use a testnet API key from the dashboard and get testnet funds from the Circle faucet.

Integration

1. Create a Layerswap swap

   Create the swap with use_depository: true for the Privy wallet address:

   curl --request POST 'https://api.layerswap.io/api/v2/swaps' \
     --header 'Content-Type: application/json' \
     --header 'X-LS-APIKEY: <LAYERSWAP_API_KEY>' \
     --data '{
       "source_network": "ETHEREUM_SEPOLIA",
       "source_token": "USDC",
       "destination_network": "ARC_TESTNET",
       "destination_token": "USDC",
       "destination_address": "<WALLET_ADDRESS>",
       "amount": 1,
       "use_depository": true
     }'
   

   use_depository: true is recommended when using Layerswap from a contract or a server wallet.

   The response includes deposit_actions with everything needed for the on-chain calls:

   {
     "data": {
       "swap": {
         "id": "...",
         "status": "user_transfer_pending",
         "requested_amount": 1,
         "source_token": { "symbol": "USDC", "contract": "0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238", "decimals": 6 }
       },
       "deposit_actions": [
         {
           "order": 0,
           "type": "transfer",
           "to_address": "<depository_contract>",
           "call_data": "<encoded_call>",
           "amount_in_base_units": "0",
           "token": { "symbol": "USDC", "contract": "0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238", "decimals": 6 },
           "encoded_args": ["<swap_id>", "<token>", "<receiver>", "0x<amount>"]
         }
       ],
       "quote": { "..." : "..." }
     }
   }
   
2. Check allowance and build the call batch

   For ERC-20 transfers, the wallet needs to approve the depository contract before the bridge call:

   import { encodeFunctionData, erc20Abi, parseUnits, toHex } from "viem";
   
   const depositAction = preparedSwap.deposit_actions.find(
     (a) => a.type.toLowerCase().includes("transfer"),
   );
   
   const requiredAmount = parseUnits(
     String(preparedSwap.swap.requested_amount),
     preparedSwap.swap.source_token.decimals,
   );
   
   const allowance = await publicClient.readContract({
     address: depositAction.token.contract,
     abi: erc20Abi,
     functionName: "allowance",
     args: [walletAddress, depositAction.to_address],
   });
   
   const bridgeCall = {
     to: depositAction.to_address,
     data: depositAction.call_data,
     value: toHex(BigInt(depositAction.amount_in_base_units)),
   };
   
   const calls =
     allowance < requiredAmount
       ? [
           {
             to: depositAction.token.contract,
             data: encodeFunctionData({
               abi: erc20Abi,
               functionName: "approve",
               args: [depositAction.to_address, requiredAmount],
             }),
             value: "0x0",
           },
           bridgeCall,
         ]
       : [bridgeCall];
   

   If allowance is already sufficient the approve call is skipped. Otherwise both calls are batched into a single sponsored wallet_sendCalls request.
3. Submit the sponsored transaction

   Submit the batched calls with Privy wallet_sendCalls and sponsor: true:

   const sendCallsResponse = await privyClient.wallets().rpc(walletId, {
     method: "wallet_sendCalls",
     chain_type: "ethereum",
     caip2: "eip155:11155111",
     sponsor: true,
     params: {
       calls,
     },
   });
   

   Privy returns a transaction_id — poll privyClient.transactions().get(transactionId) until transaction_hash is available, then use it in the next step.

4. Check the swap status

   After Privy returns the final chain transaction hash, look it up through Layerswap:

   curl \
     --header 'X-LS-APIKEY: <LAYERSWAP_API_KEY>' \
     "https://api.layerswap.io/api/v2/swaps/by_transaction_hash/<OUTER_TRANSACTION_HASH>"
   

   This maps the final transaction back to the Layerswap swap record. See the Swap Lifecycle for all possible statuses.