# Required Parameters

For the standard Universal Access Schema (UAS) buy flow, the required parameters are encoded directly in the URL path.

#### Required Path Parameters

```
https://buy.onchain.money/[chain]/[token]
```

| Parameter | Description             | Required |
| --------- | ----------------------- | -------- |
| \[chain]  | Chain identifier (slug) | Yes      |
| \[token]  | Token contract address  | Yes      |

There are no required query parameters.

***

### \[chain] — Chain Identifier

The chain parameter specifies the blockchain where execution should occur.

* Must be a supported chain slug
* Must be lowercase
* Determines execution environment and settlement context

Example:

```
ethereum
polygon
base
```

If the chain is not supported, execution will fail gracefully. \
\
See [Supported Chains](https://docs.onchain.money/getting-started/supported-chains) for details.

***

### \[token] — Token Address

The token parameter specifies the on-chain asset to execute against.

* Must be a valid contract address
* Must be lowercase
* Must correspond to the specified chain

Example:

```
0xabc123...
```

The token address is treated as a reference, not a listing or approval.

***

### Minimal Valid UAS Link

This is the smallest valid execution link:

```
https://buy.onchain.money/ethereum/0xabc123...
```

If both the chain and token are valid and supported, execution can proceed.

***

### What Is Not Required

The following are not required for execution:

* API keys
* Authentication
* Backend services
* Session state
* Query parameters
* Listings or approvals
* Attribution parameters (UTMs)

Execution is evaluated entirely at click time.

***

### Optional Parameters

Additional parameters may be included to provide context or attribution, but they do not affect execution behavior.

Examples include:

* UTM parameters for attribution
* Surface-specific metadata

See Optional Attribution Parameters (UTM) for details.

***

### Failure Behavior

If required parameters are missing, malformed, or unsupported:

* Execution does not proceed
* No partial execution occurs
* Integrators should hide or disable the execution surface when possible=

UAS is designed to fail safely and deterministically.

***

### Key Takeaway

If you can generate:

```
https://buy.onchain.money/[chain]/[token]
```

You have satisfied all required parameters for UAS execution.

Everything else is optional.