What is the (ADMIN-C) admin contact?
This FAQ explain that Admin Contact
This answer will explain the role of the “admin contact”, sometimes called the “ADMIN-C".
The admin contact is only applicable to TLDs, as it is used to verify transfers or to make modifications to the domain name. The admin contact will usually be the same as the registrant to allow the owner to maintain full control over the domain name. However, some providers set the admin contact as their own details. This is usually fine, but can cause issues if the owner wants to transfer the domain to another provider.
If you start a domain transfer to 123-reg.co.uk then we will automatically send an email to the admin contact to authorise the transfer. If this is not set to an email address you have access to or is set to your current provider, it will result in delays to the transfer of the domain.
Please note: If your contact details change (especially your email address), you can change your admin contact in the 123 Reg control panel using the “Manage Contact Details” link.