If your ESTA is denied, you cannot enter the United States under the Visa Waiver Program.
Airlines will also deny boarding if you do not have an approved ESTA or a valid visa, so you must obtain a visa before entering the country.
Ordinary travelers should apply for a B2 visa for tourism or a B1 visa for business purposes.
Regardless of the reason for the ESTA denial, a visa is required to enter the United States.
Information about the visa interview process, required documents, and appointment scheduling can be found on the official websites of the nearest U.S. Embassy or Consulate and the U.S. Department of State.
Please note that visa interview appointments are not guaranteed immediately.
You may need to check available dates and consider rescheduling your entry or changing your flight if necessary.