Undefined variable: user_id, в чем проблема?

@if(Auth::user()->id == $user_id)
       
      <form method="POST" action="">
                            <button class="btn btn-danger">Delete</button>
                            @csrf
                            @method('DELETE')
        </form>
   
   @endif

public function showUserAd($user)
    {
        $user = User::where('username', $user)->first();
        
        if(empty($user)){
            abort(404);
        }
      
        return redirect()->route('adShow', [$oneAd]);
    }

Schema::create('users', function (Blueprint $table) {
            $table->increments('id');
            $table->string('username')->unique();
            $table->string('password');
            
            $table->timestamps();
        });