Please be sure you're entering all letters and numbers that follow the (21) in your unit serial number. Most ION Audio products have a capital letter "I" near the middle of the serial number, which is often mistaken for a vertical line, the number 1, or a lowercase "L". Alternatively, certain legacy products are unable to be registered, which may cause the serial number to appear as invalid. If you are entering your serial number as listed on the product and your product is currently listed on our website, please reach out to support to assist with troubleshooting!