: A simpler, portable alternative with licenses starting around $60 .

: Single-user licenses for Modbus Slave (Witte Software) typically start at $129.00 , while Simply Modbus offers licenses for around $60.00 per program.

Download the latest version of the software from the Modbus Tools Download Page . Open the program and go to the menu or press F3 . Enter your license key in the prompt provided. This license is perpetual for the major version purchased. Regards,[Your Name/Company] Option 2: Casual Update/Notification Subject: New Modbus Slave Key for [Project Name]

The email client (Outlook/Gmail) corrupted the .lic file by adding line breaks or converting quotes to "smart quotes." Fix: Open the .lic file in Notepad. Ensure it is plain ASCII text with no extra spaces. Alternatively, request the key as a raw text string to copy/paste manually.