Drupal 8: Attaching Ajax to field reference using hook_form_alter

Question

I have three Types of Content:

• Promoteur (fr)
• Fiche Plan Action ((fr)
• Fiche Action (fr)

The "Fiche Plan Action" has a reference field to the "Promoteur" (field_nom_du_promoteur_en_questi).

The "Fiche Action" has a reference field to the "Fiche Plan d'action" (field_plan_d_action).

The creation of content types as follows: Promoteur, Fiche Plan Action and finaly Fiche Action.

I want to attach an Ajax callback to the filed (field_plan_d_action), so when I change this autocomplete field, a field of a type text was filled by a link to the "Promoteur" content automatically.

I had tried to get the object in the "Fiche Action" then from that object I get, the Object of the "Promoteur" then I update the field by a link to this "Promoteur".

Note: I tried to attach Ajax to an autocomplete (reference) and a select list. When I set a static ID to get the "Promoteur" it works, but I want to get the Object of "Fiche Plan Action" and "Promoteur "dynamically from the current form (using form_alter()).

I found just one example on the Drupal docs using select list type. for the other filed types as Date (datepicker) its not clear for me.

function nom_promoteur_form_alter(&$form, FormStateInterface $form_state, $form_id){

  if($form_id == 'node_fiche_d_action_form' || $form_id == 'node_fiche_d_action_edit_form'){

   $form['field_plan_d_action']['widget'][0]['target_id']['#ajax'] = [
      'callback' => 'myAjaxCallback',
      'disable-refocus' => FALSE,  
      'event' => 'change', 
      'wrapper'=>'edit-field-nom-du-promoteur-0-value',
    ];

   $form['field_example_select']['widget']['#ajax'] = [
      'callback' => 'myAjaxCallback',
      'disable-refocus' => FALSE,  
      'event' => 'change', 
      'wrapper'=>'edit-field-nom-du-promoteur-0-value',
    ];

  }
}  


function myAjaxCallback(array &$form, FormStateInterface $form_state) {
  //$values = $form_state->cleanValues()->getValues();

  /* fiche plan d'action (Object)*/
   $nodeFPA = $form['field_plan_d_action']['widget'][0]['target_id']['#default_value'];
  //$nidFPA = (int) $nodeFPA->nid->value;

  /* Get Promoteur Dynamically  (Object)*/
  //$promoteur = $nodeFPA->field_nom_du_promoteur_en_questi->entity;

  /* Promoteur with Static ID (Object)*/ 
  $promoteur = \Drupal\node\Entity\Node::load(2);
  $nid = $promoteur->id();      
  $nLabel = $promoteur->label();

  /* Url Alias */
  $url_alias = \Drupal::service('path_alias.manager')->getAliasByPath('/node/'. $nid);

  /* Update field  */
  $form['field_nom_du_promoteur']['widget'][0]['value']['#value'] = "<a href='$url_alias'>$nLabel </a>";

  /* Just For Test */
  //$form['field_nom_du_promoteur']['widget'][0]['value']['#value'] = " Test ";

return  $form['field_nom_du_promoteur'];

}