You need to work with an ACH processor that is providing APIs. Each processor will have their own unique API flavor, but more or less they will all look the same.
How can I get access to ACH APIs?
Which companies offer API-based ACH pay-ins and payouts?1 ansAre there APIs that support building remittance services to Nepal, India, and the rest of Southeast Asia?1 ansWhich provider offers the best API for sending payments programmatically to international users?1 ansWhich financial API should be used to build a free or near-free bank ACH transfer app similar to Venmo or Square Cash?1 ans