Save data into 2 tables cakephp 3

I am very new to Cakephp 3. I try to do saveAll function in Cakephp 3, but unsuccessful.

I have 2 tables : Merchants and Users

Relationship between this 2 tables as below:

Users hasMany Merchants, Merchants belongsTo Users

I want the create a merchant's registration form that will insert the data to both tables.

Can someone help me how to insert data into 2 different tables from 1 form using Cakephp 3?

My code as below:

 <?= $this->Form->create($merchant); ?>
<fieldset>
    <legend><?= __('Add Merchant') ?></legend>
    <?php
        echo $this->Form->input('User.id');
        echo $this->Form->input('User.username');
        echo $this->Form->input('User.password');
        echo $this->Form->input('merchant_type_id', ['options' => $merchantTypes]);
        echo $this->Form->input('name');
        echo $this->Form->input('identity_number');
        echo $this->Form->input('phone_number');
    ?>
</fieldset>
<?= $this->Form->button(__('Submit')) ?>
<?= $this->Form->end() ?>

Controller:

public function registration()
{
    $merchant = $this->Merchants->newEntity();
    if ($this->request->is('post')) {
        $merchant = $this->Merchants->patchEntity($merchant, $this->request->data, [
            'associated' => ['Users']
        ]);
        if ($this->Merchants->saveAll($merchant)) {
            $this->Flash->success('The merchant has been saved.');
            return $this->redirect(['action' => 'index']);
        } else {
            $this->Flash->error('The merchant could not be saved. Please, try again.');
        }
    }
    $users = $this->Merchants->Users->find('list', ['limit' => 200]);
    $merchantTypes = $this->Merchants->MerchantTypes->find('list', ['limit' => 200]);
    $this->set(compact('merchant', 'users', 'merchantTypes'));
}

Your helps is very appreciated. Thanks.