Implement a Goldman Sachs TxB API outbound wire payment with mTLS authentication and balance polling

Verified steps

1. Provision mTLS client certificates through the GS TxB onboarding process; configure your HTTP client to present the client certificate on every API call — GS TxB rejects connections without a valid client cert
2. Obtain an OAuth 2.0 access token using the client_credentials grant with your mTLS-authenticated client; the token is short-lived and must be refreshed before expiry — implement proactive token refresh with a small buffer (e.g., refresh at 80% of TTL)
3. Check the account balance before wire initiation via the account balance endpoint; GS TxB returns both available balance and ledger balance — use available balance for outbound payment eligibility
4. Submit the wire payment order with idempotency key, beneficiary details (name, account, routing, bank name, address), amount, currency, and your internal reference; store the GS-assigned payment ID in the response
5. Poll the payment status endpoint using the payment ID; GS TxB returns status transitions through PENDING -> PROCESSING -> COMPLETED or REJECTED; COMPLETED is not final until the Fed wire IMAD is available
6. Retrieve the IMAD from the completed payment record and store it as the authoritative settlement proof; use the IMAD for any downstream reconciliation or beneficiary confirmation