You can improve by actually having it work! If the user encounters an error, let the user know what the error was, so that it could be remed
Have you idiots ever used the feedback system? It's virtually impossible to use with a mobile device! As I type, the software searches the database for keywords, handcuffing my ability to type, and frustrating the f#@k out of me. And this is with a fast connection. I can't imagine what it would be like on a slow one.
You don't have a phone number for people to call if they encounter problems. If my first credit card doesn't work, you think the user can use another one. So only people with multiple credit cards are allowed to use your system?

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bob commented
At this point I would hope that businesses would either sue for the loss of revenue, or delay, caused by what is supposed to be convenient for the customer. Instead it leaves businesses in limbo and asking the unsavory question to their customers to produce another form of payment when the first form was not a problem but a QB problem...