If your ESTA (Electronic System for Travel Authorization) application has been denied, there are a few steps you can take:

1. Review the reason for the denial: Check the email notification you received when your application was denied, it will provide the reason for the denial. Common reasons for denial include providing false or misleading information on the application, having a criminal record, or being deemed a security risk.
2. Rectify any inaccuracies in your application: If your application was rejected because you submitted incorrect information, you can update your application and resubmit it.
3. Consult a lawyer or other qualified legal advisor:
   If your application was rejected because of your past or other reasons, you might need to speak with a lawyer or other legal professional to figure out how to appeal the decision.
4. Obtain a B-1/B-2 visa: You will not be permitted to enter the United States under the Visa Waiver Program (VWP) if your ESTA application has been rejected. Instead, you must apply for a B-1/B-2 visa at a U.S. embassy or consulate.
5. When requesting an ESTA or a visa, be truthful, accurate, and transparent to prevent complications or delays. It is essential to speak with a lawyer or other legal professional if you are unclear about your eligibility.

It’s crucial to remember that even if you are successful in appealing the denial of your ESTA application, a Customs and Border Protection (CBP) officer at the port of entry will ultimately decide whether or not to grant you entrance into the country.
Therefore, it’s crucial to be prepared with all the required paperwork and to be able to justify the refusal.