i have many to many relation in my project tasks and offices table :
task model:

public function offices(): BelongsToMany 
    {
        return $this->belongsToMany(Office::class)->withPivot('main_office'); 
    }

office model:

public function tasks(): BelongsToMany    
    {       
        return $this->belongsToMany(Task::class)->withPivot('main_office');
    }

in store function in controller:

public function store(taskRequestStore $request,TaskService $service)
    {
        $offices=Office::where([['top_office_id',null],['status',1]])->get();
        $attributes = $request->all(['Caption','TaskDsc','TaskDate','Priority_id',
                                'Type','TaskFile','FilePath','StartDate','EndDate','Deadline',
                                'Commander_id','Status_id'
                                ]);
        $tasks = $service->create($attributes);
        // dd($tasks,$offices);
        $tasks->$offices->attach([1]);
       return redirect()->back();
    }

The record is inserted in the tasks table, but an error is issued for the attach command.

when active dd :

Where is the error in my code?