For Zen Cart the Client needs a payment module created for Echeck, Tested and Functioning. There is an existing old payment module for Echeck, but its from a different processor and i am not sure if it can be used or adjusted to work. You can try this first, and if you cannot adjust this payment module to work, then you must create it from scratch. Integration info is all available. You will integrate the echeck module on a low traffic website or your test website first, and when functioning properly transfer if to the high traffic website. Low Budget.
Update: the company used for check processing is pay2check they use the check21 system
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