Laravel attempt function Error with credentials?

When i enter my email and password it return

return redirect()->back();

But i check before if condition using dd the $credentials email and password are passing the value, but it doesn't go to the attempt($credentials))

Where is the problem and why email and password is not check in if condition?

My processLogin function is

public function processLogin(Request $request)
    {

        $credentials = $request->only('seller_email');

        $credentials['password'] = $request->input('seller_password');

//        dd($credentials);

        if (Auth::guard('seller')->attempt($credentials)){
            return redirect()->intended(route('seller.dashboard'));
        }

            return redirect()->back();

    }

via Chebli Mohamed