Ensure your key is for the TCP Client and not the RTU Master or TCP Server ; they are separate products with unique licenses. Where to Get Support
These keys are generally perpetual for the version purchased, meaning no monthly subscriptions. How to Apply Your License Key Update (upd) simply modbus tcp client license key upd
Launch the Simply Modbus TCP Client executable. Ensure your key is for the TCP Client
Enter the name and the alphanumeric key exactly as provided in your purchase email. simply modbus tcp client license key upd