function block_blogspot_username($user_login, $user_email, $errors) {
    // Check if the username contains "blogspot"
    if (strpos($user_login, 'blogspot') !== false) {
        $errors->add('blogspot_error', 'Registrations with blogspot in the username are not allowed.');
    }
}

add_action('user_profile_update_errors', 'block_blogspot_username', 10, 3);
add_action('woocommerce_registration_errors', 'block_blogspot_username', 10, 3);
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