diff --git a/WEBSERVICES/ZUGFeRDRESTService/Controllers/ValidationController.cs b/WEBSERVICES/ZUGFeRDRESTService/Controllers/ValidationController.cs
index 7c03b15b..a362aa8d 100644
--- a/WEBSERVICES/ZUGFeRDRESTService/Controllers/ValidationController.cs
+++ b/WEBSERVICES/ZUGFeRDRESTService/Controllers/ValidationController.cs
@@ -9,8 +9,6 @@ using static DigitalData.Modules.Interfaces.Exceptions;
 using static DigitalData.Modules.Interfaces.ZUGFeRDInterface;
 using static DigitalData.Modules.Interfaces.PropertyValues;
 using System.Data.SqlClient;
-using DigitalData.Modules.Database;
-using Microsoft.CodeAnalysis.Operations;
 
 namespace ZUGFeRDRESTService.Controllers
 {
@@ -55,11 +53,12 @@ namespace ZUGFeRDRESTService.Controllers
         /// <summary>
         /// POST: /api/validation
         /// </summary>
-        /// <param name="files">This parameter's name needs to correspond to the html form's file-input name</param>
+        /// <param name="file">This parameter's name needs to correspond to the html form's file-input name</param>
+        /// <param name="user_id">This is the email address which the user supplied</param>
         [HttpPost]
         public ValidationResponse Post(IFormFile file, string user_id)
         {
-            _logger.Debug("Start processing request to ValidationController");
+            _logger.Info("Start processing request to ValidationController");
 
             object oDocument;
             PropertyValues.CheckPropertyValuesResult oResult = new PropertyValues.CheckPropertyValuesResult();
@@ -68,11 +67,11 @@ namespace ZUGFeRDRESTService.Controllers
             {
                 using Stream oStream = file.OpenReadStream();
                 {
-                    _logger.Debug("Extracting ZUGFeRD Data from file [{0}]", file.FileName);
+                    _logger.Info("Extracting ZUGFeRD Data from file [{0}]", file.FileName);
 
                     oDocument = _zugferd.ExtractZUGFeRDFileWithGDPicture(oStream);
 
-                    _logger.Debug("Checking ZUGFeRD Data against the database");
+                    _logger.Info("Starting structural check against the database.");
 
                     oResult = _props.CheckPropertyValues(oDocument, _propertyMap, "MESSAGEID");
 
@@ -84,7 +83,7 @@ namespace ZUGFeRDRESTService.Controllers
                     _logger.Debug("Found [{0}] required properties", oRequiredProperties.Count);
                     _logger.Debug(string.Join(",", oRequiredProperties.ToArray()));
 
-                    _logger.Debug("Result of checking against the database: {0} valid properties, {1} missing properties",
+                    _logger.Info("Result of checking against the database: {0} valid properties, {1} missing properties",
                         oResult.ValidProperties.Count, oResult.MissingProperties.Count);
 
                     if (oResult.MissingProperties.Count > 0)
@@ -95,16 +94,36 @@ namespace ZUGFeRDRESTService.Controllers
 
                     Tuple<bool, string> oValidateResult = ValidateBuyerOrderReference(oResult.ValidProperties);
 
-
-                    string oMessage = "Die hochgeladene Datei ist eine gültige-ZUGFeRD Rechnung";
-
-                    _logger.Debug($"Replying with: [{oMessage}]");
-
-                    return new ValidationResponse()
+                    if (oValidateResult.Item1 == false)
                     {
-                        status = RESPONSE_OK,
-                        message = oMessage
-                    };
+                        throw new ZUGFeRDExecption(ErrorType.UnknownError, "Die hochgeladene Datei kann nicht validiert werden, weil ein unbekannter Fehler aufgetreten ist.");
+                    }
+
+                    string oValidateResultString = oValidateResult.Item2;
+
+                    if (oValidateResultString == "ALL REFERENCES CHECKED POSITIVE")
+                    {
+                        string oMessage = "Die hochgeladene Datei ist eine gültige-ZUGFeRD Rechnung";
+
+                        _logger.Info($"Responding with message: [{oMessage}]");
+
+                        return new ValidationResponse()
+                        {
+                            status = RESPONSE_OK,
+                            message = oMessage
+                        };
+                    } else
+                    {
+                        string oMessage = oValidateResultString;
+
+                        _logger.Info($"Responding with message: [{oMessage}]");
+
+                        return new ValidationResponse()
+                        {
+                            status = RESPONSE_ERROR,
+                            message = oMessage
+                        };
+                    }
                 };
             }
             catch (ZUGFeRDExecption ex)
@@ -129,7 +148,7 @@ namespace ZUGFeRDRESTService.Controllers
                     _ => new List<string>()
                 };
 
-                _logger.Debug($"Replying with: [{oMessage}]");
+                _logger.Info($"Responding with message: [{oMessage}]");
 
                 return new ValidationResponse()
                 {
@@ -144,7 +163,7 @@ namespace ZUGFeRDRESTService.Controllers
 
                 string oMessage = "Die hochgeladene Datei kann nicht validiert werden, weil ein unbekannter Fehler aufgetreten ist.";
 
-                _logger.Debug($"Replying with: [{oMessage}]");
+                _logger.Info($"Responding with message: [{oMessage}]");
 
                 return new ValidationResponse()
                 {
@@ -156,9 +175,10 @@ namespace ZUGFeRDRESTService.Controllers
 
         private Tuple<bool, string> ValidateBuyerOrderReference(List<ValidProperty> pProperties)
         {
-
             var oMessageId = GetMessageId();
+            _logger.Debug("Created new MessageId: [{0}]", oMessageId);          
 
+            _logger.Debug("Inserting properties into database.");
             foreach (var oItem in pProperties)
             {
                 var oResult = InsertPropertyMap(oItem, oMessageId);
@@ -169,17 +189,16 @@ namespace ZUGFeRDRESTService.Controllers
                 }
             }
 
+            _logger.Debug("Calling validation prodecure.");
             try
             {
-                using SqlCommand oCommand = new SqlCommand("PRCUST_INV_CHECK_FROM_PORTAL @MESSAGE_ID, @MSG_OUTPUT");
-                oCommand.CommandType = System.Data.CommandType.StoredProcedure;
-                oCommand.Parameters.Add("MESSAGE_ID", System.Data.SqlDbType.VarChar).Value = oMessageId;
-                oCommand.Parameters.Add("MSG_OUTPUT", System.Data.SqlDbType.VarChar).Direction = System.Data.ParameterDirection.Output;
+                using SqlCommand oCommand = new SqlCommand("EXEC PRCUST_INV_CHECK_FROM_PORTAL @REF_GUID, @MSG_OUTPUT");
+                oCommand.Parameters.Add("REF_GUID", System.Data.SqlDbType.VarChar, 250).Value = oMessageId;
+                oCommand.Parameters.Add("MSG_OUTPUT", System.Data.SqlDbType.VarChar, 500).Direction = System.Data.ParameterDirection.Output;
 
                 if (_database.MSSQL.ExecuteNonQuery(oCommand))
                 {
                     string oReturnValue = (string)oCommand.Parameters["MSG_OUTPUT"].Value;
-
                     return new Tuple<bool, string>(true, oReturnValue);
 
                 }