All potential holders of a .travel name must be approved to hold that name by having their eligibility reviewed. That review of eligibility is called "authentication". .travel is giving members of selected travel associations the chance to have their authentication reviewed by their association and others to have their authentication reviewed by third party authentication providers, prior to registration.
When the review is completed you will receive a reference code/UIN if you are confirmed as eligible to hold a .travel name.
Reference code/UIN is a 16 digits number that enable for you to register .travel domain. Your Reference code/UIN is permanent and will not change. It may be revoked if your eligibility changes.
Who's your registrar? They should help you to get the code.(chargeable) I help my clients to get authenticated.
I registered but I still haven't purchased any names but I think there are a few good ones still available. It's not that hard to get approved, just write to them. It took me a couple of replies & giving them some basic info to finally get approved but it was fairly easy.
In order to register a domain name, you must be Authenticated as a legitimate service and product provider in the travel and tourism industry. As part of the Authentication Process, you will also be required to submit the .travel domain names that you intend to register. Once Authenticated, you will be provided with a valid Unique Identification Number (UIN). The UIN can then be presented to a valid .travel Registrar for the registration of your chosen .travel domain names.