Why the form does not save data from the entity reference field?

Question

I have a custom entity (with the name Entity Quote), from the add form of this entity I make a multistep form.

In the custom entity Entity Quote, I added another custom entity (with the name Quote Design) as a reference field(with the name Design) to add the form of the second custom entity Quote Design to the second form step of the first custom entity Entity Quote. And I implemented adding the form of the second custom entity using the module Inline Entity Form:
https://www.drupal.org/project/inline_entity_form

Where for the reference field I chose in the Manage Form Display the widget: Inline entity form - Complex

But the problem is that only the fields on the first step of the form are saved where the fields of the first custom entity (Entity Quote), on the second step where the two fields of the second custom entity (Quote Design) the data is not saved. The data is not in the tables and, accordingly, is not in the UI either.

The save() method is executed after pressing the Save button, which appears on the second step of the form.

Implementation of multistep form (Entity Quote add form) in sandbox:
https://phpsandbox.io/n/divine-grass-1doo-ylab7

Answer 1

As you've discovered Inline Entity From saves all the referenced entities on the final save, so you'd need to add fairly complex handling to carry its form state to page two.

If I was doing this, I would consider using a pure JS solution for your two pages, where you show and hide fields as desired. The IEF processing is pretty fancy and I wouldn't want to mess with the setup it has.