I'm not directly affiliated with Databricks, but I can offer some general advice on what you can do if you're encountering an issue with a voucher code while trying to register for the "Databricks Certified Associate Data Engineer" exam:

1. Double-Check the Voucher Code: Ensure that you've entered the voucher code correctly, paying close attention to any spaces, letters, or numbers. Voucher codes are often case-sensitive, so make sure the case matches the code you received.

2. Expiration Date: You mentioned that the voucher code is set to expire on October 1, 2023. Double-check today's date to confirm that you are within the valid timeframe for using the code.

3. Contact Databricks Support: If you've confirmed the voucher code and the expiration date but still encounter issues, it's best to contact Databricks' customer support or certification support. They can assist you with troubleshooting the issue and may be able to provide a solution or extend the voucher if there is a valid reason for the error.

4. Provide Proof: When contacting support, be prepared to provide proof of the voucher code, such as the email or notification you received with the code on May 12, 2023. This will help them verify the validity of the code.

5. Check for Specific Restrictions: Some voucher codes may have specific conditions or restrictions. Ensure that you meet all the criteria associated with the voucher, such as eligibility requirements or geographic limitations.

Databricks' support team should be able to assist you in resolving this issue promptly. They can provide guidance on the specific steps you need to take to register for the exam using your voucher code or offer an alternative solution if necessary.