diff --git a/src/SKIT.FlurlHttpClient.Wechat.Work/Converters/Internal/System.Text.Json/Long/TextualNullableLongConverter.cs b/src/SKIT.FlurlHttpClient.Wechat.Work/Converters/Internal/System.Text.Json/Long/TextualNullableLongConverter.cs
new file mode 100644
index 00000000..2cb4e65b
--- /dev/null
+++ b/src/SKIT.FlurlHttpClient.Wechat.Work/Converters/Internal/System.Text.Json/Long/TextualNullableLongConverter.cs
@@ -0,0 +1,38 @@
+using System.Text.Json.Serialization;
+
+namespace System.Text.Json.Converters
+{
+    internal class TextualNullableLongConverter : JsonConverter<long?>
+    {
+        public override long? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        {
+            if (reader.TokenType == JsonTokenType.Null)
+            {
+                return null;
+            }
+            else if (reader.TokenType == JsonTokenType.Number)
+            {
+                return reader.GetInt64();
+            }
+            else if (reader.TokenType == JsonTokenType.String)
+            {
+                string? value = reader.GetString();
+                if (string.IsNullOrEmpty(value))
+                    return null;
+
+                if (long.TryParse(value, out long l))
+                    return l;
+            }
+
+            throw new JsonException();
+        }
+
+        public override void Write(Utf8JsonWriter writer, long? value, JsonSerializerOptions options)
+        {
+            if (value.HasValue)
+                writer.WriteNumberValue(value.Value);
+            else
+                writer.WriteNullValue();
+        }
+    }
+}
diff --git a/src/SKIT.FlurlHttpClient.Wechat.Work/Models/CgibinOA/Approval/CgibinOAGetApprovalDetailResponse.cs b/src/SKIT.FlurlHttpClient.Wechat.Work/Models/CgibinOA/Approval/CgibinOAGetApprovalDetailResponse.cs
index 14976514..4060111e 100644
--- a/src/SKIT.FlurlHttpClient.Wechat.Work/Models/CgibinOA/Approval/CgibinOAGetApprovalDetailResponse.cs
+++ b/src/SKIT.FlurlHttpClient.Wechat.Work/Models/CgibinOA/Approval/CgibinOAGetApprovalDetailResponse.cs
@@ -77,6 +77,7 @@
                                 /// </summary>
                                 [Newtonsoft.Json.JsonProperty("sptime")]
                                 [System.Text.Json.Serialization.JsonPropertyName("sptime")]
+                                [System.Text.Json.Serialization.JsonConverter(typeof(System.Text.Json.Converters.TextualNullableLongConverter))]
                                 public long? ApproveTimestamp { get; set; }
 
                                 /// <summary>
@@ -258,8 +259,8 @@
                                         /// </summary>
                                         [Newtonsoft.Json.JsonProperty("s_timestamp")]
                                         [System.Text.Json.Serialization.JsonPropertyName("s_timestamp")]
-                                        [System.Text.Json.Serialization.JsonNumberHandling(System.Text.Json.Serialization.JsonNumberHandling.AllowReadingFromString)]
-                                        public long Timestamp { get; set; }
+                                        [System.Text.Json.Serialization.JsonConverter(typeof(System.Text.Json.Converters.TextualNullableLongConverter))] 
+                                        public long? Timestamp { get; set; }
                                     }
 
                                     public class SelectorControlValue
@@ -498,7 +499,8 @@
                                         /// </summary>
                                         [Newtonsoft.Json.JsonProperty("time")]
                                         [System.Text.Json.Serialization.JsonPropertyName("time")]
-                                        public long Timestamp { get; set; }
+                                        [System.Text.Json.Serialization.JsonConverter(typeof(System.Text.Json.Converters.TextualNullableLongConverter))]
+                                        public long? Timestamp { get; set; }
                                     }
 
                                     public class RelatedApprovalControlValue
@@ -594,7 +596,8 @@
                                         /// </summary>
                                         [Newtonsoft.Json.JsonProperty("time")]
                                         [System.Text.Json.Serialization.JsonPropertyName("time")]
-                                        public long Timestamp { get; set; }
+                                        [System.Text.Json.Serialization.JsonConverter(typeof(System.Text.Json.Converters.TextualNullableLongConverter))]
+                                        public long? Timestamp { get; set; }
                                     }
                                 }
 
diff --git a/test/SKIT.FlurlHttpClient.Wechat.Work.UnitTests/ModelSamples/CgibinOA/Approval/CgibinOAGetApprovalDetailResponse.json b/test/SKIT.FlurlHttpClient.Wechat.Work.UnitTests/ModelSamples/CgibinOA/Approval/CgibinOAGetApprovalDetailResponse.json
index b4c62c1a..c0669167 100644
--- a/test/SKIT.FlurlHttpClient.Wechat.Work.UnitTests/ModelSamples/CgibinOA/Approval/CgibinOAGetApprovalDetailResponse.json
+++ b/test/SKIT.FlurlHttpClient.Wechat.Work.UnitTests/ModelSamples/CgibinOA/Approval/CgibinOAGetApprovalDetailResponse.json
@@ -22,7 +22,7 @@
                         },
                         "speech": "",
                         "sp_status": 1,
-                        "sptime": 0,
+                        "sptime": 1234567890,
                         "media_id": []
                     },
                     {
@@ -31,7 +31,7 @@
                         },
                         "speech": "",
                         "sp_status": 1,
-                        "sptime": 0,
+                        "sptime": "",
                         "media_id": []
                     }
                 ]