<?php

namespace Ice\ExternalUserBundle\Form\Type;

use FOS\UserBundle\Form\Type\RegistrationFormType as BaseType;

use Symfony\Component\Form\FormBuilderInterface,
    Symfony\Component\OptionsResolver\OptionsResolverInterface;

class RegistrationFormType extends BaseType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
//        parent::buildForm($builder, $options);

        $builder
            ->add('plainPassword', 'password', array(
                'description' => 'Plain text password. Encoded before new user is persisted.',
            ))
            ->add('email', 'email', array(
                'description' => 'Email address. Must be unique.',
            ))
            ->add('title', 'text', array(
                'description' => 'Salutation.',
            ))
            ->add('firstNames', 'text', array(
                'description' => 'First name(s).',
            ))
            ->add('lastName', 'text', array(
                'description' => 'Last name.',
            ))
            ->add('dob', 'date', array(
                'widget' => 'single_text',
                'description' => 'Date of birth.',
                'required' => false,
            ))
        ;
    }

    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => 'Ice\ExternalUserBundle\Entity\User',
            'csrf_protection' => false,
            'validation_groups' => array('rest_register'),
        ));
    }

    public function getName()
    {
        return 'register';
    }
}

<?php

namespace Ice\ExternalUserBundle\Form\Type;

use FOS\UserBundle\Form\Type\RegistrationFormType as BaseType;

use Symfony\Component\Form\FormBuilderInterface,
    Symfony\Component\OptionsResolver\OptionsResolverInterface;

class RegistrationFormType extends BaseType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
//        parent::buildForm($builder, $options);

        $builder
            ->add('plainPassword', 'password', array(
                'description' => 'Plain text password. Encoded before new user is persisted.',
            ))
            ->add('email', 'email', array(
                'description' => 'Email address. Must be unique.',
            ))
            ->add('title', 'text', array(
                'description' => 'Salutation.',
            ))
            ->add('firstNames', 'text', array(
                'description' => 'First name(s).',
            ))
            ->add('lastName', 'text', array(
                'description' => 'Last name.',
            ))
            ->add('dob', 'date', array(
                'widget' => 'single_text',
                'description' => 'Date of birth.',
                'required' => false,
            ))
        ;
    }

    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => 'Ice\ExternalUserBundle\Entity\User',
            'csrf_protection' => false,
            'validation_groups' => array('rest_register'),
        ));
    }

    public function getName()
    {
        return '';
    }
}

Remove Registration form name so the name does not form part of the register JSON request body.
Remove Registration form name so the name does not form part of the register JSON request body.
