The Synergy JOIN license requires a security policy in the Local Security Policy to be set to false in order for the license to validate.
The value in the Local Security Policy is:
Security Settings > Local Policies > Security Options > System cryptography: Use FIPS compliant algorithms for encryption.
When this value is enabled, you will see the error message 'The license is not valid'.
To resolve the issue, this policy has to be set to 'Not enabled'.