using $this when not in object context

[gianmarxWebmapp]

I would like to dynamically select the parameters, in the first function $this->id gives me the following error:

using $this when not in object context

while in the second no.

below the code:

` public static function getNovaChartjsSettings(): array
{

    $r = TrelloCard::selectRaw('year(last_activity) year, monthname(last_activity) month, count(*) data')
        ->groupBy('year', 'month')
        ->orderBy('last_activity', 'asc')
        ->where('customer_id',$this->id)//using $this when not in object context 
        ->get()->pluck('month');

    return [
        'default' => [
            'type' => 'line',
            'titleProp' => 'name',
            'identProp' => 'id',
            'height' => 600,
            'indexColor' => '#999999',
            'color' => '#FF0000',
            'parameters' => $r,
            'options' => ['responsive' => true, 'maintainAspectRatio' => false],

        ]
    ];
}
public function getAdditionalDatasets(): array
{
    $r = TrelloCard::selectRaw('year(last_activity) year, monthname(last_activity) month, count(*) data')
        ->groupBy('year', 'month')
        ->orderBy('last_activity', 'asc')
        ->where('customer_id',$this->id)
        ->get();

    return [

        'default' => [
            [
                'label' => ' Month',
                'borderColor' => '#f87900',
                'fill' => '+1',
                'backgroundColor' => 'rgba(20,20,20,0.2)',//For bar charts, this will be the fill color of the bar
                'data' => $r->pluck('data'),
            ]
        ]
    ];
}`