The licensing model has evolved to support active development:
Prevents malware from making permanent changes to your system with minimal CPU/RAM impact.
As of May 2026, several tiers are available to fit different user needs: Feature Comparison - Sandboxie-Plus
Because keygens are heuristic malware. Legitimate software does not require a "key generator." Your antivirus is correct.
If you paste it into Sandboxie Plus, the software will likely reject it immediately. If it "accepts" it, you have likely installed a modified, malicious version of Sandboxie Plus. Uninstall immediately and run a Windows Defender Full Scan.