Issue with the Teams Agent Integration Dotnet App

[Arunamshu-ku]

Failed to deserialize task event System.Text.Json.JsonException
Error sending message to agent: A2AException: Failed to deserialize task event System.Text.Json.JsonException: The JSON value could not be converted to System.DateTimeOffset. Path: $.status.timestamp | LineNumber: 0 | BytePositionInLine: 280.

---> System.FormatException: The JSON value is not in a supported DateTimeOffset format.

at System.Text.Json.ThrowHelper.ThrowFormatException(DataType dataType)

at System.Text.Json.Utf8JsonReader.GetDateTimeOffset()

at System.Text.Json.Serialization.Converters.DateTimeOffsetConverter.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options)

at System.Text.Json.Serialization.Metadata.JsonPropertyInfo`1.ReadJsonAndSetMember(Object obj, ReadStack& state, Utf8JsonReader& reader)

at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)

at System.Text.Json.Serialization.Converters.JsonMetadataServicesConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)

at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)

at System.Text.Json.Serialization.Metadata.JsonPropertyInfo`1.ReadJsonAndSetMember(Object obj, ReadStack& state, Utf8JsonReader& reader)

at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)

at System.Text.Json.Serialization.Converters.JsonMetadataServicesConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)

at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value, Boolean& isPopulatedValue)

at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)

--- End of inner exception stack trace ---

at System.Text.Json.ThrowHelper.ReThrowWithPath(ReadStack& state, Utf8JsonReader& reader, Exception ex)

at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, T& value, JsonSerializerOptions options, ReadStack& state)

at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.Deserialize(Utf8JsonReader& reader, ReadStack& state)

at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.DeserializeAsObject(Utf8JsonReader& reader, ReadStack& state)

at System.Text.Json.JsonSerializer.ReadFromSpanAsObject(ReadOnlySpan1 utf8Json, JsonTypeInfo jsonTypeInfo, Nullable1 actualByteCount)

at System.Text.Json.JsonSerializer.Deserialize(JsonElement element, JsonTypeInfo jsonTypeInfo)

at A2A.A2AEventConverterViaKindDiscriminator`1.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options)

To Reproduce
Steps to reproduce the behavior:

1. Integrate a Standard Logic App conversational agent to bot framework
2. Test in Webchat section of the bot framework
3. The messages are sent successfully in the background and the logicapp workflow responds correctly as well. But the chatbot does not receive the response from logic app and shows above error.
4. This issue started from 16th December 2025. It was working fine until then

Expected behavior
The response from the logic app workflow is received by the chatbot instead of the above error

Screenshots

Desktop (please complete the following information):

• OS: Windows
• Browser Edge
• Version [e.g. 22]