If you used the MobaXterm Customizer (available only to Pro users), the license information may be "hard-coded" or "baked" directly into the generated .msi or .exe file for easier deployment. Configuration File Locations
Windows might have named the file Pro.key.txt without showing the .txt extension. Enable "File name extensions" in File Explorer. The exact name must be Pro.key (case-sensitive? No, but exact name is safest). mobaxterm professional license key location