How to add a new field to Registration form (femanager)?

I am using TYPO3 10.4 with in2code/Femanager extension to allow front end user registration and want to add a custom field to the form.

I have followed the docs about this here, and have my field in the form and I can save the field value if entered in the backend.

My problem is the field does not save the value when entered in the frontend form. I think I am missing something?

This is what I have:

/MyExtension/Configuration/Extbase/Persistence/Classes.php :

<?php

return [
    \myVendor\MyExtension\Domain\Model\User::class => [
        'tableName' => 'fe_users',
        'recordType' => 0,
    ],
];

/MyExtension/Configuration/PageTS/PageTSConfig.tsconfig :

$GLOBALS['TYPO3_CONF_VARS']['SYS']['Objects'][\In2code\Femanager\Domain\Model\User::class] = [
    'className' => \myVendor\MyExtension\Domain\Model\User::class,
];

\TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\TYPO3\CMS\Extbase\Object\Container\Container::class)
    ->registerImplementation(
        \In2code\Femanager\Domain\Model\User::class,
        \myVendor\MyExtension\Domain\Model\User::class
    );

/MyExtension/Classes/Domain/Model/User.php :

<?php

namespace myVendor\MyExtension\Domain\Model;

use TYPO3\CMS\Extbase\Domain\Model\Category;
use TYPO3\CMS\Extbase\Persistence\ObjectStorage;

class User extends \In2code\Femanager\Domain\Model\User
{

    protected string $myNewField;
    
    public function getMyNewField(): string
    {
        return $this->myNewField;
    }
    
    public function setMyNewField(string $myNewField): void
    {
        $this->myNewField = $myNewField;
    }

}

myExtension/ext_tables.sql :

CREATE TABLE fe_users (
    myExtension_myNewField varchar(255) DEFAULT '' NOT NULL,
);

myExtension/Configuration/TCA/Overrides/fe_users.php :

<?php
defined('TYPO3_MODE') || die();

$GLOBALS['TCA']['fe_users']['ctrl']['type'] = 'tx_extbase_type';
$tmpFeUsersColumns = [
   'myExtension_myNewField' => [
      'exclude' => 1,
      'label' => 'My New Field',
      'config' => [
         'type' => 'text',
      ],
   ]
];

\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addTCAcolumns('fe_users', $tmpFeUsersColumns);
\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addToAllTCAtypes('fe_users', 'myExtension_myNewField');

myExtension/Configuration/Extbase/Persistence/Classes.php :

<?php

declare(strict_types=1);

use myVendor\myExtension\Domain\Model\User;

return [
    User::class => [
        'tableName' => 'fe_users',
        'recordType' => 0,
    ],
];

myExtension/ext_localconf.php :

$GLOBALS['TYPO3_CONF_VARS']['SYS']['Objects'][\In2code\Femanager\Domain\Model\User::class] = [
    'className' => \myVendor\myExtension\Domain\Model\User::class,
];

\TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\TYPO3\CMS\Extbase\Object\Container\Container::class)
    ->registerImplementation(
        \In2code\Femanager\Domain\Model\User::class,
        \myVendor\myExtension\Domain\Model\User::class
    );

My problem was that the field name in ext_tables.sql and fe_users.php need to be named with underscores or all lowercase eg. my_new_field.

And everywhere else uses camel case eg. myNewField.

As mentioned in this answer here