This article will explain the difference between the domain contact and 123 Reg account contact.
Domain Contact
The Domain contact is the legal owner of the domain name, which can be either an individual or a company/organisation. If you are managing the domain name on behalf of another party, you would use their details as the Domain contact and yours as the Admin contact.
For help with changing your domain name’s contact details, please see the guide: How do I modify the contact information for my domain name?
Account Contact
The Account contact handles the day-to-day management of the 123 Reg user account. This is where emails relating to renewal notifications, domain expiration reminders and other important emails from 123 Reg will be sent.
For help with changing your 123 Reg Account details, please see the guide: How do I change contact details for my 123 Reg account?