If you haven't already logged into your USAePay Merchant Console and generated a source key from your account under “Settings → Source Keys → Add Source” the do so now. Place your source key in the “Merchant Key” text box with no spaces or extra characters. If you have added a
PIN on the source key place it in the “
PIN” text box with no spaces or extra characters. Hit save. Then make sure the USAePay gateway is selected in the previous window. The radial button should be checked.