This capability was introduced into Odoo version 15.

To use it:

1. For each BANK Journal you wish to use to Pay Vendors, complete the NACHA configuration section of the Outgoing Payments tab:

Note: The information is normally provided by your Bank once you have been approved to send payments via ACH.

Immediate Destination: This field contains the routing number of your bank or credit union. 

Destination: This field contains the name of your bank or credit union.

Immediate Origin: This field contains your 9-digit company ID (EIN) unless your bank specifies otherwise.

Company Identification: This field contains a 10-digit number made up of your company ID (EIN), with an additional number at the start, often a 1 but you should check with your bank in case it is a different number.

Originating DFI Identification: The Depository Financial Institution field contains your assigned 8 digit number. 

2. Record each payment and use the NACHA payment Method.  It is important to understand the cutoff for same-day payments. The file you generate will need to have either a future date for each payment, or be sent before the cutoff if the dates match today's date.

3. Once you have created all the Payments you want to include in a NACHA file (one per Bank), you would select them all from the Payments screen and choose CREATE BATCH PAYMENT from the ACTION Menu:

4. Open the Batch Payment and switch to the EXPORTED FILE tab to access the file:

If you need to make any adjustments you can click "Re-generate Export File" to re-create a new file to download.

Note: You may find this video (similar workflow, but for SEPA in Europe) useful: