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

# Corridors and assets

> Which rail and token pairs are supported, how assets are identified, and how amounts work.

## Corridors

A **corridor** is a source asset → destination asset pair.

Whether a corridor settles depends on which routes settlement providers are actively covering. [Supported networks](/get-started/reference/supported-networks) lists the configured chains and assets; the authoritative live answer is the gateway's own `/v1/defaults`, which omits any chain it cannot pay on.

## Asset identifiers

Every asset in a payment request uses a standard identifier string that specifies both the chain and the token contract:

```
{chain_id}/{token_standard}:{contract_address}
```

Examples:

* USDC on Arbitrum Sepolia: `eip155:421614/erc20:0x75faf114eafb1BDbe2F0316DF893fd58CE46AA4d`
* USDT on Tron Shasta: `tron:shasta/trc20:TG3XXyExBkPp9nzdajDZsozEu4BkaSJozs`

You can't pass just `"USDC"` — the exact identifier is required. Copy them from [Supported networks](/get-started/reference/supported-networks) or your sandbox profile.

## Token amounts

Amounts in the API are **whole numbers in the token's smallest unit** — not decimal dollars.

| USDC (6 decimals) | API value |
| ----------------- | --------- |
| 0.01 USDC         | `10000`   |
| 0.10 USDC         | `100000`  |
| 1.00 USDC         | `1000000` |

## Next steps

After you finish this page, the following go deeper:

* [Supported networks](/get-started/reference/supported-networks)
* [Glossary](/get-started/reference/glossary)