Hi there! I understand you're having trouble connecting to myGuichet using the LuxTrust app on your Mac running OS X 10.15. Let’s work through this together.

To start, can you let me know if you see any specific error messages when trying to connect through the LuxTrust app? Also, are you attempting this through a browser or directly on the app installed on your device? This info will help me guide you better.

Meanwhile, here’s a general step-by-step you can try to troubleshoot the connection:

1. Restart your Mac: This simple step can clear temporary issues that might be blocking the connection.

2. Check your internet connection: Make sure your Mac is connected to a stable internet network.

3. Ensure your LuxTrust app is up to date: Since you are on OS X 10.15, verify the app version is compatible and updated.

4. Try unlinking and relinking your device:
- Log in to your myGuichet.lu account via your browser.
- Click on 'Link a device' and choose 'Unlink my device' to remove the current connection.
- Then, follow the steps to link your device again, either by scanning a QR code or by using the LuxTrust product linking methods.
This process can refresh the connection between the myGuichet service and your LuxTrust app1.

5. Check for port conflicts on your Mac: LuxTrust Middleware uses port 24727. If another app is using this port, it can cause connection issues.
- You can check active ports by using Terminal with the command: lsof -i :24727
- If you find another app using this port, closing or reconfiguring that app might help2.

6. Verify LuxTrust Mobile App activation: If you're using the mobile app, make sure it's activated properly on your smartphone as per the guide provided by LuxTrust7.

If after trying these steps, the connection issue persists, please let me know the exact behavior or error messages. Also, if you recently updated your system or the app, that could be relevant.

Are you comfortable trying these steps now? I’m here to help you through any of them.