# Open & Fund a Channel

## Overview

Opening a channel locks a deposit of a TIP-20 token between a payer and a payee. The payer funds the
channel up front, and that deposit bounds how much can be paid out through vouchers. You can add more
funds later with a top-up, and read the channel's state at any time.

[See the Payment Channels guide](https://docs.tempo.xyz/guide/machine-payments/pay-as-you-go)

## Recipes

These recipes assume you have [set up a Tempo client](/tempo).

### Open a Channel

Open and fund a channel with [`channel.openSync`](/tempo/actions/channel.open). The deposit is taken
from the payer (your account) in the given TIP-20 token.

:::code-group
```ts twoslash [example.ts]
import { parseUnits } from 'viem'
import { client } from './viem.config'

const result = await client.channel.openSync({
  deposit: parseUnits('100', 6),
  payee: '0x742d35Cc6634C0532925a3b844Bc9e7595f0bEbb',
  token: '0x20c0000000000000000000000000000000000001',
})
```

```ts twoslash [viem.config.ts] filename="viem.config.ts"
// [!include ~/snippets/tempo/viem.config.ts:setup]

// [!include ~/snippets/tempo/viem.config.ts:channel]
```
:::

### Top Up a Channel

Add more deposit to an open channel with [`channel.topUpSync`](/tempo/actions/channel.topUp).

:::code-group
```ts twoslash [example.ts]
import { parseUnits } from 'viem'
import { channel, client } from './viem.config'

const result = await client.channel.topUpSync({
  additionalDeposit: parseUnits('50', 6),
  channel,
})
```

```ts twoslash [viem.config.ts] filename="viem.config.ts"
// [!include ~/snippets/tempo/viem.config.ts:setup]

// [!include ~/snippets/tempo/viem.config.ts:channel]
```
:::

### Read Channel State

Read the current state of a channel with [`channel.getStates`](/tempo/actions/channel.getStates),
including its deposit and settled amount.

:::code-group
```ts twoslash [example.ts]
import { channel, client } from './viem.config'

const state = await client.channel.getStates({ channel })
```

```ts twoslash [viem.config.ts] filename="viem.config.ts"
// [!include ~/snippets/tempo/viem.config.ts:setup]

// [!include ~/snippets/tempo/viem.config.ts:channel]
```
:::

## Best Practices

### Size the Deposit to Expected Volume

The deposit caps total payouts until you top up. Fund the channel for the volume you expect over its
lifetime so the payee is not forced to settle and reopen mid-stream, while avoiding locking up more
than you need.

### Reuse a Channel for Many Payments

The whole point of a channel is to amortize the onchain cost over many off-chain vouchers. Open once
per payer/payee relationship and keep it open, rather than opening a new channel per payment.

### Persist the Channel Identity

You need the channel's fields (payer, payee, token, salt) to sign vouchers and settle later. Persist
them after opening so both sides can reconstruct the same channel.

## See More

<Cards>
  <Card icon="lucide:receipt" title="Send & Settle Vouchers" description="Pay through the channel with signed off-chain vouchers." to="/tempo/guides/payment-channels/vouchers" />

  <Card icon="lucide:circle-x" title="Close & Withdraw" description="Close the channel and reclaim the remaining deposit." to="/tempo/guides/payment-channels/close" />

  <Card icon="lucide:square-function" title="channel.topUp" description="Add more deposit to an open channel." to="/tempo/actions/channel.topUp" />

  <Card icon="lucide:book-open" title="Tempo Docs: Payment Channels" description="The channel deposit and voucher model." to="https://docs.tempo.xyz/guide/machine-payments/pay-as-you-go" />
</Cards>