Hello, first of all, thank you for your reply. I often see your comments. Regarding the problem I encountered, since I am a beginner, I might make some basic mistakes. I have a global state that contains a list of Messages [accumulating]. My decision node will send a tool call (tool_call) to add to the Messages list in the state. After calling the tool node, a ToolMessages is concatenated to the state. It seems like a ToolMessage must follow a tool_call? I am calling in parallel, which causes a tool_call to receive another tool_call? Is this causing the error? I don’t quite understand. Do I need to merge the decision node and the tool call node, packaging tool_call and ToolMessages together? Would that solve the problem?