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PowerShell one-liner:
Get-ItemProperty -Path "HKCU:\Software\Think-Cell\License" -Name "LicenseKey" -ErrorAction SilentlyContinue | Select-Object -ExpandProperty LicenseKey
Note: The license key stored in the registry is often encoded or hashed. It may not appear as the plain-text alphanumeric string you received in your email. think cell license key registry
License key, right-click in the right pane → New > String Value.Key (case-sensitive).Key and paste your license string.