How to resolve mass assignment error in laravel?

I am new to the laravel, i am implementing user registration api while registering the user it's throwing an error like mass_assignment

Add [first_name] to fillable property to allow mass assignment on [App\\Entities\\User].

User.php

<?php

namespace App;

use Illuminate\Notifications\Notifiable;
use Illuminate\Contracts\Auth\MustVerifyEmail;
use Illuminate\Foundation\Auth\User as Authenticatable;

class User extends Authenticatable
{
    use Notifiable;

    protected $table ='user';
    /**
     * The attributes that are mass assignable.
     *
     * @var array
     */
    protected $fillable = [
        'first_name','last_name','phone_number','email'
    ];

    protected $guarded =[];
    /**
     * The attributes that should be hidden for arrays.
     *
     * @var array
     */
    protected $hidden = [
        'password', 'remember_token',
    ];

    /**
     * The attributes that should be cast to native types.
     *
     * @var array
     */
    protected $casts = [
        'email_verified_at' => 'datetime',
    ];
}

UserController.php

 public function userRegister(userRequest $request){
        $data = $this->repository->create($request->all());     
        return $user = new UserTransformer($data);                     
    }
}

please help why this error is happening ..?

The main problem is laravel5.8 the model paths are different so use following facade

use App\modelname

instead of use App\Entities\User,let me know if this resolves your problem :-)