backpack-for-laravel Error install backpack for Laravel 5.3

class ImportacionesCrudController extends CrudController
{
    private $api;

    public function __construct(webApi $api) {
        $this->api = $api;
        return parent::__construct();
    }

    public function setUp()
    {
        $this->api->sendValidation();
        ....

// add this to the use statements 
use App\Models\Task;

// Notice: You need to add this to "create" function as well, I'm just writing here the update function to keep it short.
 public function update(UpdateRequest $request)
    {
$redirect_location = parent::updateCrud($request);
foreach ($request->machines as $machine) {
            $set= array('m'=>'0','t'=> '0', 's' => '0', 'a' => '0');
            if (isset($request['m'])) in_array ($machine, $request['m']) ? $set['m'] = '1' :  $set['m'] = '0';
            if (isset($request['t'])) in_array ($machine, $request['t']) ? $set['q'] = '1' :  $set['q'] = '0';
            if (isset($request['s'])) in_array ($machine, $request['s']) ? $set['b'] = '1' :  $set['b'] = '0';
            if (isset($request['a'])) in_array ($machine, $request['a']) ? $set['y'] = '1' :  $set['y'] = '0';

            Task::find($request->id)->machines()->syncWithoutDetaching([$machine => $set]);
return $redirect_location;
        }

// Code explanation:
// what we are doing basically here is to grab the $request data
// For example: In the $request we receive m[3] b[1,3] y[1] arrays
// meaning that for our task:
// Machine 1 has no monthly, no quarterly but biannual and yearly checkboxes checked
// Machine 3 has monthly, no quarterly, biannual and no yearly checkboxes checked
// with the loop above, we cast that incoming data into this structure
// $set would contain after the loop:
// '1' => ['m' => '0', 'q'=> '0', 'b' => '1', 'y' => '1']
// '3' => ['m' => '1', 'q'=> '0', 'b' => '1', 'y' => '0']

// with that, we updated the intermediate table using syncWithoutDetaching

<div @include('crud::inc.field_wrapper_attributes') >
   <label>{!! $field['label'] !!}</label>
   @include('crud::inc.field_translatable_icon')
   <select
       name="{{ $field['name'] }}[]"
       style="width: 100%"
       id="select2_ajax_multiple_custom_{{ $field['name'] }}"
       @include('crud::inc.field_attributes', ['default_class' =>  'form-control'])
       multiple>

       @if ($old_value)
           @foreach ($old_value as $item)
               @if (!is_object($item))
                   @php
                       $item = $connected_entity->find($item);
                   @endphp
               @endif
               <option value="{{ $item->getKey() }}" selected>
                   {{ $item->{$field['attribute']} }}
               </option>
           @endforeach
       @endif
   </select>
// What I added is:
   <div id="freq">
   @if ($old_value)
           @foreach ($old_value as $item)
               @if (!is_object($item))
                   @php
                       $item = $connected_entity->find($item);
                   @endphp
               @endif
               <div id="div{{ $item->getKey() }}">
               <span>{{ $item->{$field['attribute']} }} -- </span>
               Monthly <input type="checkbox" id="m{{ $item->getKey() }}" name="m[]" value="{{ $item->getKey() }}" @php if ($item->pivot['m'] == "1") echo "checked"; @endphp > 
               Quarterly <input type="checkbox" id="q{{ $item->getKey() }}" name="q[]" value="{{ $item->getKey() }}" @php if ($item->pivot['q'] == "1") echo "checked"; @endphp> 
               Biannual <input type="checkbox" id="b{{ $item->getKey() }}" name="b[]" value="{{ $item->getKey() }}" @php if ($item->pivot['b'] == "1") echo "checked"; @endphp> 
               Yearly <input type="checkbox" id="y{{ $item->getKey() }}" name="y[]"value="{{ $item->getKey() }}" @php if ($item->pivot['y'] == "1") echo "checked"; @endphp> <br/>

               </div>
           @endforeach
       @endif
   </div>


// js code to add or remove rows containing the checkboxes (This needs to be put inside <script> tags obviously)    $("#select2_ajax_multiple_custom_machines").on("select2:select", function(e) {
// add checkbox row
           htmlRow = "<div id=\"div"+e.params.data.id+"\">"+"<span> "+e.params.data.text+"-- </span>"+" Monthly <input type=\"checkbox\" id=\"m"+e.params.data.id+"\" name=\"m[]\" value=\""+e.params.data.id+"\">";
           htmlRow += " Quarterly <input type=\"checkbox\" id=\"q"+e.params.data.id+"\" name=\"q[]\" value=\""+e.params.data.id+"\">";
           htmlRow += " Biannual <input type=\"checkbox\" id=\"b"+e.params.data.id+"\" name=\"b[]\" value=\""+e.params.data.id+"\">";
           htmlRow += " Yearly <input type=\"checkbox\" id=\"y"+e.params.data.id+"\" name=\"y[]\" value=\""+e.params.data.id+"\"><br/>";
           htmlRow += "</div>";
           $("#freq").append(htmlRow);  
       });

$("#select2_ajax_multiple_custom_machines").on("select2:unselect", function(e) {
// remove checkbox row
           $("#div"+e.params.data.id).remove(); 
});