> ## Documentation Index
> Fetch the complete documentation index at: https://jiffyscan.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Error AA21: Prefund Payment Failure

> Handling insufficient native tokens for gas costs

Without a paymaster, the `sender` address lacks sufficient native tokens for the user operation's gas costs.

## Potential Fixes

1. If not using a paymaster, ensure the `sender` has enough native tokens. Use functions like [`getRequiredPrefund`](/permissionless/reference/utils/getRequiredPrefund):

```typescript theme={null}
const neededPrefund = getRequiredPrefund({
    userOperation
})
const accountBalance = await public.fetchBalance({
    address: userOperation.sender
})
if (accountBalance < neededPrefund) {
    throw new Error(`Insufficient native tokens in sender address`)
}
```

2. To use a paymaster for gas fees, set the paymasterAndData field:

```typescript theme={null}
const operationHash = await bundler.submitUserOp({
    paymasterAndData: "0x3b912be0270b59143985cc5c6aab452d99e2b4bb0000000000000000000000000000000000000000000000000000000064c0957400000000000000000000000000000000000000000000000000000000000000007d99385d8ef0af67affbf9944df8c121e9d1f6aef8dd82a4aeb5db310c42d3dc5b51c9e0835d94c3b22564d3d94f0e1d14e37571e46651da8de567d128a361a01b",
    // Other user operation details...
})
```