@chriscastellaniYou went through the merchant services with your bank? Typically they will be involved in the setup. It may be something that you don’t have access to or wouldn’t be able to guess at. Have you been able to verify with any of the customers getting this error that their cards do in fact have funds? I would call your merchant services and see what insights they may have. The specific rep responsible for setting up your account would be best. See if they have any records of these transactions being attempted.
The “Gateway Refused Transaction” is odd. And that your customers often get “an error occurred during processing” is another giveaway that something funny is going on, I think. I’ve ran well over 1,000 test transactions, and I when you get that message it is always something funny. It will be sometimes programming errors, using the wrong post url, and one friend from here I did some programming work for had his client verify with their MSP and they were the issue.
Another possibility is that you do not have your http addresses redirected to https. The form won’t load correctly and work if it’s called from an http address. It may be that you are entering https:// on your browser (or you have in the past and it autocompletes) and your affected customers are using an http address. The issue you describe makes it sound like there is something specific to you that is right that is wrong for your customers. It could be a daily transaction limit imposed by your MSP for some reason, the secure url you enter and that they do not, they for some reason let their browser sit idle for 20 minutes and their payment token expires,....
There are not many valid reasons that your transactions should go through and your customers systematically fail.