I have a site with Drupal 8 and Commerce 2. Now trying to build a custom "Create new order" -form for admin. Created a custom module and form with buildForm() function. Managed to add selection for store and user (as entity reference fields) but I got stuck when trying to add products for order. I had an idea to use inline entity form for this, but I can't figure out how to do that.
In buildForm() function I have
$form['products']['ief'] = [ '#type' => 'inline_entity_form', '#entity_type' => 'commerce_order_item', '#bundle' => 'default', '#form_mode' => 'default', '#op' => 'add' ]
This shows 3 fields (Product variation auto complete field, quantity and unit price) but it does not show "Create new order item"-button. Should this work out-of-box and is there something wrong with field settings...?
Or do I need to add submit button and some ajax callback myself to generate new fieldset?
Any help is appreciated :)