American Express, once known for offering exceptional customer support, gets a failing grade in handling a simple, human mistake. Here are the details: I own several small online businesses. Our VeriSign online merchant gateway was purchased by PayPal, so PayPal recently informed us that we needed to switch over using their API on our web sites. Last week our programmers finished rewriting EventMingle to use the new PayPal Gateway API. Credit card companies give us test credit card numbers to use when testing the gateway to make sure it works correctly. They test to make sure it rejects invalid credit cards,...