> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.6mm.com/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.6mm.com/_mcp/server.

# Secrets & Signing

<h2 id="signing-rule">
  Signing rule
</h2>

Signed requests exclude sign, omit empty values, sort fields by ASCII key order, join fields as k=v\&k2=v2, and calculate HMAC-SHA256 hex with apiSecret.

<h2 id="sdk-managed-fields">
  SDK-managed fields
</h2>

| Field     | Source              | Description                                    |
| --------- | ------------------- | ---------------------------------------------- |
| agentCode | SDK config          | Partner agent code.                            |
| timestamp | Current server time | Unix timestamp in seconds.                     |
| nonce     | Secure random value | Replay-protection random string.               |
| sign      | HMAC-SHA256         | Request signature.                             |
| currency  | Default currency    | Used when transfer/account APIs omit currency. |