How to regain date type data from an array of date in _joinData

I have users table and calendars table joining with calandars_users table.
Users can join events of calendars, and calendars_users table has a date type column ‘subscribed’ of registered date.

But, I can not pacth entry nor new entry getted.

[⟩ Cake\Controller\Component\SecurityComponent->_validatePostCORE/src/Controller/Component/SecurityComponent.php, line 124]#)

says:

Missing field ‘calendars.1._joinData.subscribed’ in POST data

Request data on debug_kit is:

calendars (array)
->1 (array)
–> id 1
–>_joinData (array)
—>subscribed (array)
---->year 2018
---->month 08
---->day 01

How can I get date type format from date array in _joinData?
Thanks in advance.

p.s.
If not _joinData, date array is patched and saved automatically.

Are you using Cake view/form helpers to make the date field?

You are using CakePHP 3.x ?

Thanks, hakim.

Cakphp version is 3.6.11.
Data fields were made by form helper.
foreach($event_data as $id=>$data){

<?= $this->Form->select(“calendars.{$id}.id”, $events, [
‘empty’ => ‘選択’,
‘value’ => …
]) ?>
<?= $this->Form->input(“calendars.{$id}._joinData.subscribed”, [
‘type’ => ‘date’,
‘dateFormat’ => ‘YMD’,
‘empty’ => ‘—’,
‘value’ => …
]) ?>
}
This is assigend to markstory in issues. I’ll report here after his reproduction test.