Unique Phone number

[nitaish]

WHMCS only sets the email addresses as unique for a customer as the email address is also the user name of the client. However, anybody can sign up as different customers using the same phone number. We want to restrict a single account creation per phone number so that nobody can enter the phone number in the clientarea if there is already another client with the same phone number. Can anybody help me to achieve this?

[ishizaki]

add hook

add_hook('ClientDetailsValidation', 1, function($vars) {
    $error_message = array();

    // uniq phone number check
    
    return $error_message;
});