Implement Plaid Signal to evaluate ACH debit risk before originating a transfer

Verified steps

1. After linking a user's bank account via Plaid Link and obtaining an access_token and account_id, POST /signal/evaluate before creating any ACH debit transfer; include the access_token, account_id, client_transaction_id (your idempotency key), amount, and user identity fields
2. Parse the evaluate response: scores.customer_initiated_return_risk.score (0–99) and scores.bank_initiated_return_risk.score indicate likelihood of a return; recommended_action (PROCEED, CAUTION, BLOCK) provides a suggested decision
3. Map your internal risk thresholds to the Signal scores; a typical implementation PROCEEDs below a customer_initiated score threshold, CAUTIONs (adds a hold) in a middle band, and BLOCKs above a high-risk threshold
4. If you proceed with a transfer, call POST /signal/decision/report immediately after originating the ACH to report your decision and the actual transfer ID; this feedback loop improves Signal model accuracy for your portfolio
5. Call POST /signal/return/report when an ACH return is received; include the client_transaction_id and the NACHA return code — this closes the feedback loop and is required by Plaid's Signal terms of service
6. Combine Signal scores with your own velocity rules (e.g., count of debits in last 30 days) for a layered risk decision; do not rely on Signal as the sole control