An error has occurred while processing SubReport 'subReportDetails':
Unable to establish a connection to the database. Please verify that your connection string is valid. In case you use a named connection string from
the application configuration file, make sure the name is correct and the connection string settings are present in the configuration file of your
application.
------------- InnerException -------------
Initialization string format is out of specification starting at index 0.

 protected override void OnNeedDataSource(object sender, EventArgs e)
        {
            base.OnNeedDataSource(sender, e);

            var report = sender as Telerik.Reporting.Processing.Report;

            //// Report Post Formatting.

            // Apply Sorts.
            if (report.Parameters["Sortings"].Value != null)
            {
                Common.ApplySort(this, report.Parameters["Sortings"].Value.ToString());
            }
}

public static void ApplySort(Report report, string sortingColumns)
        {
            // sorting Columns string format: ColumnName:Asc;ColumnName:Desc
            if (sortingColumns == null)
                return;

            foreach (var item in sortingColumns.Split(','))
            {
                // Get The field value for the column to sort by... IE. SellthroughValuePercent is an iff calculation.
                report.Report.Sortings.Add(new Sorting
                {
                    Expression = string.Format("=Fields.[{0}]", item.Split(':')[0]),
                    Direction = item.Split(':')[1] == "Asc" ? SortDirection.Asc : SortDirection.Desc,
                });
            }
        }

 // Create report source
                    var reportSource = new Telerik.Reporting.UriReportSource
                    {
                        Uri = Server.MapPath("Manifest.trdp") // Replace "PathToYourReport" with the actual path to your report
                    };
                    // add parameters to report source
                    reportSource.Parameters.Add(new Telerik.Reporting.Parameter("@shipmentId", shipmentsId.Value.ToString()));                                       

                    // Create report processor
                    var reportProcessor = new Telerik.Reporting.Processing.ReportProcessor();
                    
                     // Render the report to PDF
                     var result = reportProcessor.RenderReport("PDF", reportSource, null);

                    if (result.HasErrors)
                    {                        
                        throw new Exception("There were errors during report processing: " + result.Errors[0].Message.ToString());
                    }

                    // Set the content type to PDF
                    Response.ContentType = "application/pdf";

         
                    // Write the PDF data to the output stream
                    Response.OutputStream.Write(result.DocumentBytes, 0, result.DocumentBytes.Length);

                    // End the response to force it to client
                    Response.End();

Fields.ProductionDate.ToString("Y", CultureInfo.GetCurrentCulture("bg-BG"))

=Fields.ProductionDate

...
services.TryAddSingleton<IReportServiceConfiguration>(sp => new ReportServiceConfiguration
{
    ReportingEngineConfiguration = sp.GetService<IConfiguration>(),
    HostAppId = "BlazorWebReportDesignerDemo",
    Storage = new FileStorage(),
    ReportSourceResolver = new UriReportSourceResolver(Path.Combine(sp.GetService<IWebHostEnvironment>().WebRootPath, "Reports"))
});