As in most countries, the final decision is made by immigration officers at the port of entry. You can apply online by filling out the application form under esta.cbp.dhs.gov and paying a fee. If you are denied boarding or denied entry to the U.S. port of entry, you will continue to be subject to our cancellation fee in accordance with the terms of our contract with you. For more details on the Visa Waiver program, see the Visa Waiver program information on the U.S. Embassy usembassy.org.uk website. We advise you to take your ESTA authorization with you on a trip and register at least 72 hours before departure. Please note that if you are registering for ESTA, you must have a valid passport at the time of registration.
If you applied for a post-date passport (for example. B to reflect a change of name), this passport is only valid on the date of entry into force indicated in the passport….