We no longer want our custom API form to process ACH transactions. We figured that by disabling the ACH option in the LO shadow form, it would prevent future attempts, or at least produce an error message. We found that ACH continues to process despite that change.
The payment type in the shadow form is ignored for the Donate API calls. The solution would be to eliminate ACH as a payment option in the customization/API form. Blackbaud does have developers on staff that might be able to assist in making this change to the code. Contact your account manager for more details.