Your processor (most likely Applied Merchant Systems) may have enabled the BuyPass platform on your account. This platform looks back at the past 20 transactions and declines them if they are duplicate. Authorize.net has a similar process that you can disable in their control panel but it only goes back a few minutes. If you are getting a 318 error, it is most likely due to BuyPass.

You can choose to disable BuyPass by contacting your processor (Applied Merchant) and asking them to disable it.