langgraph-tutorial.ipynb: AttributeError: 'tuple' object has no attribute 'invoke' i need help

Title: AttributeError: 'tuple' object has no attribute 'invoke' when using OpenRouter with LangChain on Colab Issue Description: I encountered the following error when running my LangChain app in Google Colab: AttributeError: 'tuple' object has no attribute 'invoke' The only change I've made to the original code is replacing the LLM with an OpenRouter model: llm = ChatOpenAI( model="openai/gpt-4o-mini", openai_api_base="https://openrouter.ai/api/v1", temperature=0 ) The traceback points specifically to the invocation of the LLM: classification = llm.invoke([message]).content.strip() Full error traceback: --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) <ipython-input-65-872f2bc002f1> in <cell line: 0>() 5 6 state_input = {"text": sample_text} ----> 7 result = app.invoke(state_input) 8 9 print("Classification:", result["classification"]) 6 frames <ipython-input-62-2b776fbd1895> in classification_node(state) 6 ) 7 message = HumanMessage(content=prompt.format(text=state["text"])) ----> 8 classification = llm.invoke([message]).content.strip() 9 return {"classification": classification} 10 AttributeError: 'tuple' object has no attribute 'invoke' Could anyone help identify why this is happening? Thanks!