private string EncodeExternalApiLink = "https://blabla.dk";
private string EncodeExternalApiLinkPostFilter = "searchstring/blabla/api/search";

[HttpPost("getdata/filtered")]
        public async Task<IActionResult> GetDataFromExternalFiltered([FromBody] string filter)
        {
            var filterString = new StringContent(filter);

            EncodeExternalToken token = GetExternalToken().Result;
            using (var client = new HttpClient())
            {
                client.BaseAddress = new Uri(EncodeExternalApiLink);

                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("text/plain"));
                client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token.access_token);

                using (var response = await client.PostAsync(EncodeExternalApiLinkPostFilter, filterString))
                {
                    return Json(response);
                    if (response.IsSuccessStatusCode)
                    {
                        string content = await response.Content.ReadAsStringAsync();

                        return Content(content, "application/json");
                    }
                    else
                    {
                        return NotFound();
                    }
                }
            }
        }