Thanks for contacting Syncfusion support.
Syncfusion license keys are version specific and platform specific. You can use the v16.3 unlock key for main release, nuget release and service pack release in v16.3.
If you are upgrading to latest release v16.4, you should generate the license key for v16.4 and use the same key for other releases in v16.4.
Kalap Johnson Peter P.