Sponsored Transactions

This section covers how to do sponsored transactions with the Aptos .NET SDK.

It’s important that you understand the basics of building transactions. If not, refer to the guide below for more information.

1. Set up your AptosClient

   Set up your Aptos client by adding the Aptos namespace and instantiating an AptosClient. You can use a predefined configuration from Networks or configuring your own.

   using Aptos;
   
   class Program
   {
       static void Main(string[] args)
       {
           var config = new AptosConfig(Aptos.Networks.Mainnet);
           var client = new AptosClient(config);
       }
   }

2. Set up the Accounts

   To create a sponsored transaction, it’s important that there is a sponsor and a user. In this example:

   • The user: Will be the account that is sending APT to the recipient.
   • The sponsor: Will be the account that pays for gas fees of the transaction.

   using Aptos;
   
   class Program
   {
       static void Main(string[] args)
       {
           var config = new AptosConfig(Aptos.Networks.Devnet);
           var client = new AptosClient(config);
   
           // 1. Create accounts and fund it them.
           var user = Account.Generate();
           var recipient = Account.Generate();
           var sponsor = Account.Generate();
   
           await client.Faucet.FundAccount(user.Address, 100_000_000);
           await client.Faucet.FundAccount(sponsor.Address, 100_000_000);
       }
   }

3. Build the Transaction

   You can now build the transaction using the AptosClient. In the transaction, its important that you enable the withFeePayer flag to enable the sponsored transactions.

   using Aptos;
   
   class Program
   {
       static void Main(string[] args)
       {
           ...
   
           // 2. Build the transaction
           var transaction = await client.Transaction.Build(
               sender: account,
               data: new GenerateEntryFunctionPayloadData(
                   function: "0x1::aptos_account::transfer_coins",
                   typeArguments: ["0x1::aptos_coin::AptosCoin"],
                   functionArguments: [account.Address, "100000"]
               ),
               // It's important to set this flag to true to enable sponsored transactions
               withFeePayer: true
           );
       }
   }

4. Sign the Transaction using both accounts

   Have both the user and the sponsor sign the transaction. This ensures that the sponsor has agreed to pay for the transaction and the user has agreed to execute the transaction. When signing with the sponsor, the SignAsFeePayer method is used instead.

   using Aptos;
   
   class Program
   {
       static void Main(string[] args)
       {
           ...
   
           // 3. Sign the transaction with the user
           var userSignature = client.Transaction.SignTransaction(transaction);
   
           // 4. Sign the transaction with the sponsor
           var feePayerSignature = client.Transaction.SignAsFeePayer(feePayer, transaction);
       }
   }

5. Submit the Transaction

   Once the transaction is signed by both the user and the sponsor, it can be submitted to the blockchain. The AptosClient can be used to submit the transaction.

   using Aptos;
   
   class Program
   {
       static void Main(string[] args)
       {
           ...
   
           // 5. Submit the transaction
           var submitTransactionData = new SubmitTransactionData(transaction, userSignature, feePayerSignature);
           var submittedTransaction = await client.Transaction.SubmitTransaction(submitTransactionData);
       }
   }

6. Wait for the Transaction to Execute

   After the transaction has been submitted, it will have to process before its committed to the blockchain. The AptosClient can be used to wait for the transaction to be processed and executed.

   using Aptos;
   
   class Program
   {
       static void Main(string[] args)
       {
           ...
   
           // 6. Wait for the transaction to be processed
           var transactionResult = await client.Transaction.WaitForTransaction(submittedTransaction.Hash);
       }
   }

7. Print Balances

   After the transaction has committed to the blockchain, you can print the balances of the user and the recipient.

   using Aptos;
   
   class Program
   {
       static void Main(string[] args)
       {
           ...
   
           // 7. Print balances
           var userBalance = await client.Account.GetCoinBalance(user.Address);
           var feePayerBalance = await client.Account.GetCoinBalance(feePayer.Address);
           var recipientBalance = await client.Account.GetCoinBalance(recipient.Address);
           Console.WriteLine($"User {user.Address} has {userBalance?.Amount ?? 0} APT");
           Console.WriteLine($"FeePayer {feePayer.Address} has {feePayerBalance?.Amount ?? 0} APT");
           Console.WriteLine($"Recipient {recipient.Address} has {recipientBalance?.Amount ?? 0} APT");
       }
   }

   The result should look like this:

   User 0xffd89f1e2fef8c67cfb1b99d58ea799281f1d1a0a178db49c3eacab2fe7c0735 has 99900000 APT
   FeePayer 0x842ca7d995255ee73186a6793d6bde7c983c528be7b1a25e1614f4eddb744d4c has 99900100 APT
   Recipient 0x823010a52a589ef528d14ebee4a4af56a00f0ae8afba135c9268581a960e21d7 has 100000 APT

   The user sent 0.001 APT to the recipient leaving the user with 0.999 APT. The sponsor paid for the gas fees of the transaction leaving the sponsor with 0.999001 APT.