How to update SalesChannel correctly in Shopware6

Question

I try to update shipping method. I know, that I finally have to update SalesChannel with new Shipping object, but I will get error:

1. [/] Expected data to be array.

#[NoReturn]
private function assignShippingObject(object $shippingObject): void
{
    $salesChannels = $this->database->readTableSalesChannel(Context::createDefaultContext());

    foreach ($salesChannels as $salesChannel) {

        $shippingMethods = $salesChannel->getShippingMethods();

        $shippingMethods->add($shippingObject);
        $salesChannelData[] = [
            'id'              => $salesChannel->getId(),
            'shippingMethods' => $shippingMethods
        ];
        $this->database->updateSalesChannel(Context::createDefaultContext(), $salesChannelData);
    }
}

If I try like this:['shippingMethods' => $shippingMethods] I will get error:Argument #1 ($key) must be of type string, int given, 'cause first key in array is 0,now! Also this will not fix my problem:'shippingMethods' => $shippingMethods->getIds()

Any idea, how to update SalesChannel with shipping object - $shippingObject - ?

If I will try like this....

 $salesChannelData[] = [
            'id' => $salesChannel->getId(),
            'shippingMethods' => ['id'=>'018ddbaf0ac3762797b951b4ab908282']
        ];

...I will get error: