Quote Originally Posted by nerdgirlie View Post
About once a week, I get 2 receipts from Authorize.net from the same person in the same minute. I only get ONE order from zen cart, but the credit card is charged twice, both transactions within seconds of each other.

What Authorize.net says: Each charge is sending them a separate invoice. The customer may have clicked the SUBMIT ORDER button twice. These are not being identified as duplicate transactions since they have separate Invoice numbers.
i'm a bit curious here. if you have 2 charges at authorize.net with separate invoice numbers, and only 1 order in zen-cart, what has happened to the second invoice number sent to authorize.net? does that invoice/order number NOT exist on your zen-cart system? if it does not, do you have missing invoice/order numbers in your orders table?

in my experience dealing with authorize.net, they are rarely, if ever, at fault. they effectively process whatever you send them.

i think the solutions presented here are all sound, but if authorize.net says they have separate invoice numbers for the transactions, it should not be too hard to track that back to your ZC orders table, and see if those orders exist.

good luck!