RAILS
Sandbox

First rail in production: Argentina

B2B payment rails for your system.

Payment accounts in Argentine pesos with a CVU (an Argentine virtual account number), immediate transfers through COELSA (the Argentine clearing house), holder validation, and signed events and webhooks. One API, one stable contract.

Start in the sandboxSee the reference

A signed request · sandbox
POST /v1/outgoing_transfers HTTP/1.1
Host: empresas-sandbox.fcmpayments.com
Authorization: Bearer fcm_test_…
Content-Type: application/json
Idempotency-Key: 7c1d9a54-…
Content-Digest: sha-256=:…:
Signature-Input: sig1=("@method" "@target-uri" "content-type"
  "content-digest" "idempotency-key");created=…;nonce="…";keyid="ck_…";alg="ed25519"
Signature: sig1=:…:

{"account_id":"acc_…","amount":100000,"currency":"ARS",
 "destination":{"type":"alias","value":"sbx.valida"},
 "expected_counterparty_cuit":"27000000006"}

What Grip Rails does

  • Peso accounts with a CVU

    Each account has its balance, read from the ledger at the time of the request, and one or more CVUs.

    • GET/v1/accounts
    • GET/v1/account_numbers

  • Immediate transfers through COELSA

    Outgoing to any Argentine bank account (CBU), virtual account (CVU) or alias, with authorization and a hold before moving a single peso. Incoming, each credit posted with its event.

    • POST/v1/outgoing_transfers
    • GET/v1/incoming_transfers

  • Holder validation

    Before sending, you confirm that the destination exists, is active and belongs to whom you expect.

    • POST/v1/counterparty_validations

  • Signed events and webhooks

    A contiguous sequence per entity to reconcile without gaps. Webhooks signed with JWS and keys published in a JWKS.

    • GET/v1/events
    • GET/.well-known/jwks.json

  • Idempotency on every write

    Every POST carries an Idempotency-Key. If the response is lost, you repeat the same request with the same key.

    • GET/v1/idempotency_keys/{key}

  • Sandbox with simulations

    Incoming credits, rail results and its own clock to test every path without real money.

    • POST/v1/simulations/incoming_transfers
    • POST/v1/simulations/clock/advance

Before you write code

Amounts
Integers in cents of Argentine pesos: 150000 is ARS 1,500.00. The only currency is ARS.
Authentication
An API key in Authorization: Bearer and an HTTP signature (RFC 9421) on every request with your Ed25519 or P-256 private key. The private key never leaves your system.
Idempotency
Idempotency-Key required on every POST. Never make up a new key to retry.
Reconciliation
GET /v1/events?after_sequence=N. The sequence is contiguous per entity: if you received 41 and then 43, you are missing 42.
Errors
An error object with type, code, message and retryable. If retryable is true, repeat the same request with the same key.

Environments

EnvironmentBase URL
Productionhttps://api.fcmpayments.comProduction. Real money; transfers through COELSA are irreversible. Enabled per client.
Sandboxhttps://empresas-sandbox.fcmpayments.comSandbox. Simulated ledger and rail; it never moves real money.

More about sandbox and production →

Where to go next