[BUG] Memory cannot be saved when using mem0

### Description

### problem
External memory was designated using memory0. However, an error occurs that information cannot be stored in memory.

### Steps to Reproduce

1. set some value for MEM0 api key, openai api key, url(in my case, it is azure open ai)
2. Create the source code as a test.py file
3. Run as **python test.py**.

### Expected behavior

I hope the memory is saved normally in mem0.

### Screenshots/Code snippets

### source code
```python
from crewai import Crew, Agent, Task, Process, LLM
from dotenv import load_dotenv
import os
from pathlib import Path
from crewai.memory.external.external_memory import ExternalMemory

# external storage
os.environ["MEM0_API_KEY"] = ""  # Required: MEM0 API key

load_dotenv()

chat_agent = Agent(
    role="Friendly chatbot assistant",
    goal="Engage in useful and interesting conversations with users while remembering context.",
    backstory="You are a kind and knowledgeable chatbot assistant. You excel at understanding user needs, providing helpful responses, and maintaining engaging conversations. You remember previous interactions to provide a personalized experience.",
    llm=LLM("azure/gpt-4.1"),
    verbose=True
)
chat_task = Task(
    description="Respond to user conversation. User message: {user_msg}",
    expected_output="Contextually appropriate, helpful, and friendly response.",
    agent=chat_agent
)
external_memory = ExternalMemory(
    embedder_config={
        "provider": "mem0",
        "config": {
            "user_id": "user-123",
            "org_id": "", # Required: MEM0 org_id
            "project_id": "", # Required: MEM0 project_id
        }
    }
)
chat_crew = Crew(
    agents=[chat_agent],
    tasks=[chat_task],
    process=Process.sequential,
    external_memory=external_memory,
    verbose=True,
    embedder={
        "provider": "openai",
        "config": {
            "api_key": "",  # Required: Azure OpenAI API key
            "api_base": "",  # Required: Azure OpenAI API base
            "api_type": "azure",
            "api_version": "2023-05-15",
            "model": "text-embedding-ada-002",
            "deployment_id": "text-embedding-ada-002"
        }
    }
)

def chat_loop():
    while True:
        user_msg = input(">>")
        if user_msg.lower() in {"quit", "exit"}:
            break

        bot_reply = chat_crew.kickoff(inputs={"user_msg": user_msg})

        print("🤖 > ", bot_reply)

if __name__ == "__main__":
    print("👋 Hello! Welcome to the interactive chatbot. Type 'quit' or 'exit' to end the conversation.")
    chat_loop()
```

### Operating System

macOS Sonoma

### Python Version

3.12

### crewAI Version

0.140.0

### crewAI Tools Version

0.49.0

### Virtual Environment

Venv

### Evidence

### terminal output
```zsh
HTTP error occurred: Client error '400 Bad Request' for url 'https://api.mem0.ai/v1/memories/'
For more information check: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/400
Failed to add to external memory: API request failed: {"messages":["Expected a list of items but got type \"str\"."]}
🚀 Crew: crew
├── 📋 Task: a9d3cb2f-48be-4688-a15e-73f5a0a8fa9a
│   Assigned to: Friendly chatbot assistant
│   Status: ✅ Completed
│   └── 🧠 Memory Update Overall
│       └── ❌ External Memory Memory Save Failed
└── ✅ Memory Retrieval Completed
    └── Sources Used
        └── ✅ External Memory (181.02ms)
```

### Possible Solution

None

### Additional context

The mem0 api version was tested on both v1 and v2. The same results were obtained.

Labels: bug
State: closed