Skip to main content
App Kit lets you collect a custom fee from your end users each time they spend from a Unified Balance. Custom fees can only be configured for spend transactions on destination blockchains, not deposits on source blockchains. To learn how custom fees fit into the overall fee breakdown, see How Unified Balance fees work.
If you use this feature, Arc keeps 10% of the custom fee you collect from your end users.

​
Prerequisites

Before you begin, ensure that you’ve: These are required so any example below runs with a valid kit and adapter.

​
Set a custom fee on a spend

This example spends 1.00 USDC from Base Sepolia and adds a 0.01 USDC custom fee on the spend:
TypeScript
import { AppKit } from "@circle-fin/app-kit";
import { createViemAdapterFromPrivateKey } from "@circle-fin/adapter-viem-v2";

const kit = new AppKit();

const adapter = createViemAdapterFromPrivateKey({
  privateKey: process.env.EVM_PRIVATE_KEY as string,
});

const result = await kit.unifiedBalance.spend({
  amount: "1.00",
  from: {
    adapter,
    allocations: [{ amount: "1.00", chain: "Base_Sepolia" }],
  },
  to: {
    adapter,
    chain: "Arc_Testnet",
    recipientAddress: "0xRecipientAddress",
  },
  config: {
    customFee: {
      value: "0.01", // 0.01 USDC collected as fee
      recipientAddress: "0xYourFeeWalletAddress",
    },
  },
});