API, requests, не получается собрать запрос, ошибка 403

 private async Task<List<CampaignIdFromOzon>> CreateCampaign(List<CampaignForCreate> campaigns, TokenClass token)
        {
            CampaignIdFromOzon cid;
            List<CampaignIdFromOzon> campaignIdList = new List<CampaignIdFromOzon>();
            HttpClient httpClient = new HttpClient();
            httpClient.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", token.access_token);
            HttpRequestMessage request = new HttpRequestMessage();
            HttpResponseMessage response = new HttpResponseMessage();
            request.RequestUri = new Uri("https://performance.ozon.ru:443/api/client/campaign/cpm/product");//https://performance.ozon.ru:443/api/client/campaign/cpm/product
            request.Method = HttpMethod.Post;
 
            foreach (CampaignForCreate campaign in campaigns)
            {
                request.Content = new StringContent("{\"title\":\"" + campaign.title + "\",\"dailyBudget\":\"" + campaign.dailyBudget + "\",\"placement\":\"" + campaign.placement + "\",\"expenseStrategy\":\"" + campaign.expenseStrategy + "\"}",
                    Encoding.UTF8, "application/json");
 
                response = httpClient.PostAsync(request.RequestUri, request.Content).Result;
 
                if (response.StatusCode != HttpStatusCode.OK)
                {
                    MessageBox.Show(response.StatusCode.ToString());
 
                    break;
                }
 
                cid = await response.Content.ReadAsAsync<CampaignIdFromOzon>();//не стринг, а список кампаний: https://docs.ozon.ru/api/performance/#operation/ListCampaigns
                if (cid.campaignId != "")
                    campaignIdList.Add(cid);
                //MessageBox.Show(cid.campaignId);
            }
            return campaignIdList;