If you are encountering an "invalid code" issue with your Celestron StarSense Explorer, follow these steps to resolve it:

1. Check Insert Card: Make sure you are using the correct unlock code that is typically found on the orange 4" x 6" insert card included with your Celestron packaging. Confirm that you have not misread or mistyped any part of the code.

2. App Settings: Go to the settings within the StarSense Explorer app. Tap on "Unlock Code" to see if the app displays the code that is currently being used. This might help you determine if you are indeed entering the wrong code - learn more.

3. Contact Celestron Support: If the code you have is indeed invalid and you cannot locate a new valid one, you should contact Celestron's Technical Support. Provide them with proof of purchase, and they may issue you a new unlock code. You can reach them through their support page here - learn more.

4. Troubleshoot Potential Issues: If you purchased the telescope used or if the insert card is damaged or missing, old codes may also be invalid. Verify that the code has not been previously activated on another device, as many codes are single-use per device - learn more.

5. Follow Up: If you've received a new code or your situation has not been resolved, consider following up with Celestron support as they can provide assistance tailored to your issue - learn more.

By systematically checking your code, ensuring you are using it correctly, and reaching out to support if necessary, you should be able to resolve the issue with your Celestron StarSense Explorer.