1 - set required fields https://wwws.echo-inc.com/ISPGuide-Fields2.asp
2 - counter field shouldn't be just a random integer (but it does need to
3 fallback to that as B:OP doesn't require it)
6 #echeck use customer_org and account_type to generate ec_account_type
8 - check HTTPS response code and die if not 200?
9 - order_type & ccexp_month,ccexp_year setting fiddling ->{_content} directly
10 - 'echo_reference', 'security_result', 'mac', and 'decline_code' fields...?
12 - handle returning correct is_success and error_message values in the
13 special case for AVS-only transactions we don't handle yet (B:OP needs a
14 name for that transaction!)