If you provide how your License Key is configured in appsettings.json (with key scrubbed out) I can verify if it’s ok or not.
I would check you don’t have any conflicting keys registered elsewhere, e.g. in your Environment variables, you should also clean bin/ and obj/ folders to clean out existing artifacts and do a clean rebuild. Registering the License Key before your AppHost in Program.cs should work unless there’s some conflict like incompatible .dll references.
If that doesn’t help, we’ll need someway to repro the issue, e.g. a link to a stand-alone repro on GitHub.