# How Radar prevents ACH and SEPA Direct Debit payment fraud

[Stripe Radar](https://stripe.com/radar) helps prevent fraud for ACH and SEPA Direct Debit (DD) payments that use the [Payment Intents API](https://docs.stripe.com/payments/ach-direct-debit/migrating-from-charges). Radar screens these payments by default for most users without any additional development time or action required.
### How does Radar decide payments are fraudulent?
Radar performs real-time evaluations using machine learning algorithms to help identify and block high-risk transactions. Our machine learning trains specifically for ACH and SEPA, so Radar is effective at detecting fraud that might be unique to those payment methods.
### When does Radar block payments?
All Radar products include a default [block rule](https://docs.stripe.com/radar/rules) that blocks ACH and SEPA DD payments identified as high-risk by our machine learning algorithms.
### Can I customize how Radar blocks payments?
Yes, with [Radar for Fraud Teams](https://stripe.com/radar/fraud-teams) users can:
* Create and manage [lists](https://docs.stripe.com/radar/lists) of information used to block or allow payments in [the Dashboard](https://dashboard.stripe.com/settings/radar/lists).
* Create custom [rules](https://docs.stripe.com/radar/rules) to block or allow payments based on business logic in [the Dashboard](https://dashboard.stripe.com/radar/rules).
* Use [unique attributes](https://docs.stripe.com/radar/rules/supported-attributes) to create rules for a specific payment method.
### Why was a specific payment blocked by Radar?
From the [Stripe Dashboard Transactions page](https://dashboard.stripe.com/payments), click on a transaction to open its details page. The Recent activity section shows why a payment was blocked and if it was blocked by a Radar rule.