SharePoint 2016 error 500 (internal server error)

Hello Everyone, i am facing an issue with Sp16 when i upload many documents using rest API. when i upload many documents each one is 20mb i am receiving error 500 Internal server error.
any idea about this error and how to solve it?
i tried this https://www.vioreliftode.com/index.php/how-to-make-sharepoint-2016-not-fail-long-running-uploads-large-files/ but it didn't work for me. any other suggesstions?
my post request is below

public async Task<bool> Save(string requestUri, HttpContent content)
        {
            var credential = new System.Net.NetworkCredential(
                username,
                password,
                domain);



            using (var handler = new HttpClientHandler() { Credentials = credential, UseProxy = false })
            {
                using (var client = new HttpClient(handler))
                {
                    client.DefaultRequestHeaders.Accept.Clear();



                    var mediaType = new MediaTypeWithQualityHeaderValue("application/json");



                    mediaType.Parameters.Add(new NameValueHeaderValue("odata", "nometadata"));



                    client.DefaultRequestHeaders.Accept.Add(mediaType);



                    client.DefaultRequestHeaders.Add("X-RequestDigest", await this.GetRequestDigest());
                    client.DefaultRequestHeaders.Add("binaryStringRequestBody", "true");



                    string postUrl = this.siteUrl.EndsWith("/") ? $"{this.siteUrl}{requestUri}" : $"{this.siteUrl}/{requestUri}";
                    this.logger.LogDebug("Executing SharePointService.Save: PostUrl={0}.", postUrl);



                    HttpResponseMessage response = await client.PostAsync(postUrl, content);



                    response.EnsureSuccessStatusCode();



                    this.logger.LogDebug("Executed SharePointService.Save: PostUrl={0}", postUrl);



                    return true;
                }
            }
        }