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Pay for your onchain transactions

Setting up fees is essential for your app to interact with both EVMx and supported blockchains. You need to manage one fee parameter that handles two payment scenarios: EVMx execution costs and onchain transaction sponsorship.

info

TestUSDC is currently the only supported token for converting into EVMx credits. See available TestUSDC contract address per chain here.

How the fee system works​

The fee system uses a single fees parameter that serves dual purposes:

  • Minimum deposit requirement: Users must deposit at least this amount before initiating transactions
  • Maximum fee limit: Sets an upper bound on transaction costs to protect users from excessive charges

When users deposit tokens, they are converted to credits on EVMx and allocated for both native transactions and onchain fees.

Configure fee amount​

Set up the fee amount for your app:

uint256 fees = 10 ether; // Both minimum required deposit and maximum fee limit

Fee parameter details​

The fees value controls:

  1. Minimum Required Balance: Users must deposit at least this amount to ensure transmitters are compensated for including transactions in batches.

  2. Maximum Fee Protection: Acts as an upper limit for transaction costs. Users only pay the actual cost if it's less than this amount.

Usage across transaction types​

EVMx Transactions

  • Manages fees for offchain computational processing
  • Ensures sufficient user balance for computational costs
  • Provides predictable fee structure for offchain operations

Onchain Transactions

  • Controls standard blockchain transaction fees
  • Manages gas costs for contract interactions
  • Provides fee limits for user protection

Apply fee configuration​

Set the fee configuration in your contracts:

AppGateway(appGatewayAddress).setFees(fees);

Alternatively, set fees in the AppGateway constructor:

SomeAppGateway gateway = new SomeAppGateway(addressResolver, fees, owner);

Deposit tokens to pay for transactions​

Understanding deposits and credits​

When you deposit tokens using the FeesPlug contract, they're stored in a vault and converted to credits on EVMx.

Example using depositToFeeAndNative:

  • Deposit: 100 TestUSDC → 100 credits
  • Allocation: 10 credits for native EVMx transactions, 90 credits for onchain fees

Example using depositToFee:

  • All deposited tokens are allocated exclusively for onchain fees

Deposit methods​

Method 1: Deposit for both Fees and Native transactions

cast send <CHOSEN_CHAIN_FEES_PLUG> "depositToFeeAndNative(address,address,uint256)" \
    <TOKEN_ADDRESS> \
    $APP_GATEWAY \
    <AMOUNT> \
    --rpc-url $RPC_URL \
    --private-key $PRIVATE_KEY

Method 2: Deposit for Fees only

cast send <CHOSEN_CHAIN_FEES_PLUG> "depositToFee(address,address,uint256)" \
    <TOKEN_ADDRESS> \
    $APP_GATEWAY \
    <AMOUNT> \
    --rpc-url $RPC_URL \
    --private-key $PRIVATE_KEY

Cross-chain deposits​

You can deposit tokens from multiple chains (Arbitrum, Base, Optimism, etc.) to the same AppGateway:

  • Deposits: Tokens are stored in individual FeesPlug contracts on each chain
  • Credits: A global fees manager tracks balances across all chains and converts them to EVMx credits
  • Withdrawals: You can withdraw from any chain with sufficient token balance, regardless of the original deposit location
warning

Cross-Chain Withdrawal Notice: The current implementation allows withdrawing from any chain with available balance, which could potentially be misused. This will be refined in future versions.

Additional resources​