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

> ## Agent Instructions
> Before reading these docs, install the relevant Circle Skill to get pre-loaded context — skills are LLM-optimized and cover architecture decisions, correct flows, and common pitfalls. In Claude Code: run /plugin marketplace add circlefin/skills then /plugin install circle-skills@circle. With Vercel Skills CLI: run npx skills add circlefin/skills. Available skills: use-usdc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md (balances, transfers, approvals on EVM and Solana); EURC has no skill — see https://developers.circle.com/stablecoins/what-is-eurc.md; bridge-stablecoin https://github.com/circlefin/skills/blob/master/plugins/circle/skills/bridge-stablecoin/SKILL.md (crosschain transfers via CCTP, USDC, EURC, and third-party assets); use-arc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md (Arc chain config, contract deployment, USDC bridging — Arc docs: https://docs.arc.io/llms.txt); use-circle-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md (choose wallet type); use-developer-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md (custodial wallets for payouts and treasury); use-user-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md (embedded wallets with Web2 login); use-modular-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md (smart contract wallets with passkeys and ERC-4337); use-gateway https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md (unified USDC balance, nanopayments); use-smart-contract-platform https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md (deploy, interact, monitor contracts). Pair any skill with the Circle MCP server for live SDK signatures, contract addresses, and chain IDs: {"mcpServers":{"circle":{"url":"https://api.circle.com/v1/codegen/mcp"}}}.
> Read the product overview first. Each product has an overview explaining when and why to use it. Read it before quickstarts.
> Pick the right wallet type. Developer-controlled (you hold keys), user-controlled (end user holds keys via PIN/social login), or modular (smart contract wallets with passkeys). See https://developers.circle.com/wallets.md.
> Use CCTP V2 for crosschain transfers. CCTP natively transfers USDC and EURC via burn-and-mint, and supports permissionless wrapping of third-party assets via lock-and-mint. V1 is legacy; always use V2 unless V1 is specified or the chain requires it (Noble, Sui, and Aptos still require V1). Migration guide: https://developers.circle.com/cctp/migration-from-v1-to-v2.md.
> Use Bridge Kit for frontend bridging. Wraps CCTP with a simpler SDK for user-facing apps. Use CCTP directly for backend transfers.
> Gas Station vs Paymaster. Gas Station sponsors gas for Circle Wallet transactions. Paymaster lets users pay gas in USDC. Different use cases — read both overviews.
> Gateway Nanopayments for sub-cent payments. Gasless USDC micropayments down to $0.000001 via x402 and batched settlement. For pay-per-request APIs, AI agent payments, streaming.
> Look up USDC addresses per chain. Never hardcode — use https://developers.circle.com/stablecoins/usdc-contract-addresses.md.
> Prefer SDKs over raw API calls. Node.js and Python SDKs handle auth, retries, and errors.
> API key required. Bearer token in Authorization header. Testnet and mainnet use separate keys and may use different base URLs depending on the product.
> Set up webhooks when available. Most operations are async. Webhooks deliver transaction confirmations and state changes.
> When calling list endpoints, paginate using pageSize and pageAfter until no nextPageAfter cursor is returned—stopping at the first page silently misses records.
> Building an AI agent? Start with the Agent Stack—Circle CLI, agent wallets, and nanopayments built for autonomous use cases: https://developers.circle.com/agent-stack.md.

# Conditional logic

> Understand how Nature of Business and JSON Schema conditionals control which fields are required

The End User Onboarding schema uses JSON Schema `if/then` constructs to express
conditional requirements. Not all sections and fields apply to every
application. The schema defines what is required based on the application's
configuration.

## Nature of business

The primary conditional driver is **Nature of Business (NOB)**. This
classification is set during application creation and determines which sections
and fields appear. For example, a `cryptoExchange` application may require
different documentation than a `trust` application.

## How conditionals work

The `allOf` array in the schema contains `if/then` blocks:

* The `if` clause checks the value of a parent field (most commonly
  `nature_of_business`).
* When the condition is met, the `then` clause adds fields to the `required`
  array, making them mandatory.

Supported condition types:

| Condition | Description |
| - | - |
| Exact string match | A field equals a specific value |
| boolean match | A field is `true` or `false` |
| `enum` (OR) | A field matches any value in a list |
| `contains` | An array field contains a specific value |
| Negation | A field does not match a value |

The following example shows an exact string match condition:

```json theme={null}
{
  "if": {
    "properties": {
      "natureOfBusiness": { "const": "cryptoExchange" }
    }
  },
  "then": {
    "properties": {
      "cryptoExchangeLicenseNumber": {
        "type": "string",
        "minLength": 1
      }
    },
    "required": ["cryptoExchangeLicenseNumber"]
  }
}
```

In this example, when `natureOfBusiness` is `cryptoExchange`, the schema
requires the `cryptoExchangeLicenseNumber` field. The same `if`/`then` pattern
applies to all condition types in the preceding table. Substitute the
appropriate JSON Schema keyword (`enum` for OR lists, `contains` for array
membership, `not` for negation) in the `if` block.

## Conditional side effects

After
[saving a section](/cpn/managed-payments/end-user-onboarding/howtos/create-and-populate-applications#step-4-save-section-data)
that contains a conditional parent field (for example, `beneficialOwnersExist`),
other sections may activate or deactivate. This includes
[array sections](/cpn/managed-payments/end-user-onboarding/concepts/array-sections),
which can be conditionally activated. The API signals this through two
mechanisms:

1. **`sectionsChanged` flag**: Returned in every save response. When `true`, the
   section list has changed and you should re-fetch sections.
2. **Updated `sections` array**: The response includes the current status of all
   active sections, not just the one you saved.

<Warning>
  Always check the `sectionsChanged` flag after saving section data. If you ignore
  it, your integration may submit incomplete applications or miss newly required
  sections.
</Warning>

## Mutually exclusive groups

Some conditionals create mutually exclusive branches. For example, different
variants of `basic_business_info` may exist for different NOB values. Only one
branch's fields are required at a time. The schema enforces this automatically.

## Design considerations

* Integrations that skip re-fetching after a `sectionsChanged` response risk
  submitting incomplete applications.
* Client-side validation against the schema (`minLength`, `pattern`, `enum`)
  before submitting reduces round-trips and improves the user experience.
* Use the `?resolved=true` query parameter on the schema endpoint to retrieve a
  pruned view containing only the fields that are currently active based on
  previously submitted data. This removes the need to evaluate conditional rules
  locally.