php - I received Using $this when not in object context error in Laravel

one text

I'm getting a Using $this when not in object context error in my function which just needs to divide the current numbers by the current rate. My function code:

    public function autoRanksCurrency ()
    {
        $ranks = Ranks::get();
        foreach ($ranks as $rank) {
            $bets = $rank->bets;
            $deposit = $rank->deposit;
            $reward = $rank->reward;
            $bonus = $rank->bonus;
            $update = Ranks::update([
                'bets' => $rank->bets / $this->config->kurs
            ]);
            $update->save();
        }
    }

$this->config comes from my database. Where can beaproblem?

i already try some variants, but nothing works.

UPD:

I make dd($this->config), and here is what i received:

App\Models\Config {#494 ?�?
  #table: "config"
  #fillable: array:10 [?��]
  #connection: "mysql"
  #primaryKey: "id"
  #keyType: "int"
  +incrementing: true
  #with: []
  #withCount: []
  +preventsLazyLoading: false
  #perPage: 15
  +exists: true
  +wasRecentlyCreated: false
  #escapeWhenCastingToString: false
  #attributes: array:49 [?��]
  #original: array:49 [?��]
  #changes: []
  #casts: []
  #classCastCache: []
  #attributeCastCache: []
  #dates: []
  #dateFormat: null
  #appends: []
  #dispatchesEvents: []
  #observables: []
  #relations: []
  #touches: []
  +timestamps: true
  #hidden: []
  #visible: []
  #guarded: array:1 [?��]
}

How i understand, function understand $this->config variable.