Laravel how to query a pivot table created_at timestamp equal to a date

I have users and habits, and a habit_user table to join them.

I am querying like this:

$track = $h->userAnswers()->where('user_id', Auth::user()->id)->wherePivot('created_at', '=', Carbon\Carbon::now()->subDays($i))->first();

This is running in a loop that is counting back for 7 days. there is a record in the db that is created_at: 2018-10-23 04:48:44

In my habit model I have the method you'd expect:

public function userAnswers()
{
    return $this->belongsToMany('App\Habit', 'habit_user_answers')->withTimestamps()->withPivot('answer_one', 'created_at')->orderBy('pivot_created_at', 'desc');

}

Why won't query get a record?

via Chebli Mohamed