feat: add userTransfer method for internal account transfers

[alexonconceicao]

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Title

feat(rest): add userTransfer to enable internal transfers between LN Markets accounts

Summary

This PR adds the userTransfer method to the REST client, enabling internal transfers between LN Markets accounts via POST /user/transfer with required authentication. The method is now exported in createRestClient.

Context and Motivation

This PR exposes the official internal transfer route, enabling:

• Automated rebalancing between accounts
• Splitting deposits across subaccounts
• Internal settlement without on-chain withdrawals

Main Changes

• Implemented userTransfer(data) in src/rest.ts
• Forwards the provided payload to POST /user/transfer
• Added export in createRestClient

Code snippet:

const userTransfer = (data: any) => {
  return request({
    method: 'POST',
    path: '/user/transfer',
    requireAuth: true,
    data,
  });
};

Export:

userTransfer,

API

Endpoint: POST /user/transfer
Auth: required

Example request body:

{
  "to": "user_or_account_identifier",
  "amount": 100000
}

Example response:

{
  "transferId": "abc123",
  "status": "accepted",
  "amount": 100000
}

Usage

Node.js:

import { createRestClient } from '@ln-markets/api';

const client = createRestClient({ key: process.env.LNM_KEY, secret: process.env.LNM_SECRET });

const res = await client.userTransfer({
  to: 'targetUser',
  amount: 100000
});

console.log(res);

cURL:

curl -X POST https://api.lnmarkets.com/user/transfer \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_TOKEN" \
  -d '{"to":"targetUser","amount":100000}'

Design Considerations

• Consistent with existing client pattern: thin wrapper, no local validation
• Backward compatible: only adds a new method
• Idempotency and rate limiting are handled server-side
• Errors bubble up through request()

Documentation

• Add to REST methods section of the library with minimal usage example
• Clarify authentication requirements and supported payload fields

Checklist

• Implemented with requireAuth
• Exported in createRestClient
• Generic typing for compatibility

Impact

Low risk. This change only exposes an existing API endpoint, without modifying current methods or behavior.

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