Troubleshooting Amazon Bedrock Chat Model Error with Automatically Passthrough Binary Images in n8n

Below is a summary of steps to troubleshoot and resolve the error:

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Issue Recap

When using the Amazon Bedrock Chat model via the AI Agent Tool with the "Automatically Passthrough Binary Images" option, you get the error:

"A conversation must alternate between user and assistant roles. Make sure the conversation alternates between user and assistant roles and try again."

In previous n8n versions (like 1.58.2) this worked, but in version 1.72.1 the conversation’s structure now appears to be strictly validated.

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What the Error Means

The error indicates that the underlying model expects a valid conversation history where messages alternate between the user and the assistant. This requirement means every user message needs to be followed by an assistant message and vice versa.

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Recommended Troubleshooting Steps

1. Review Conversation Structure

   • Ensure that your workflow’s payload is generating a conversation history where messages are clearly marked with roles (i.e., "user" and "assistant") and these alternate.
   • If using expressions or dynamic values, verify they resolve correctly (i.e., no null values).

2. Manually Define the Prompt

   • Instead of relying solely on the automatic passthrough, switch the Prompt option from Take from previous node automatically to Define below.
   • This allows you to explicitly build and control the conversation, ensuring that message roles are correctly ordered.

3. Check Binary Data Handling

   • Review how the binary images are passed through the node.
   • If the binary data interferes with the conversation structure or causes unexpected data formatting (e.g., null values), consider creating a dedicated node to process binary images separately from conversation text.

4. Test with a Simplified Payload

   • Set up a minimal test where you manually construct a conversation sequence with an initial user message, followed by a dummy assistant reply.
   • Once confirmed working, integrate the binary image passthrough piece by piece to identify any corruption in the conversation structure.

5. Adjust to the New Validation

   • It’s possible that later versions of n8n (1.72.1 and beyond) enforce stricter rules for conversation formatting.
   • Updating your conversation construction to meet these stricter standards should resolve the issue without reverting to an older workflow setup.

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Example

If you decide to manually define the prompt, your node might be configured similarly to:

JSONCopied
{
  "prompt": [
    { "role": "user", "content": "Hello, how can I get help with my image processing?" },
    { "role": "assistant", "content": "Sure! Please provide the image details." }
  ]
}

Ensure that when additional messages are passed in, they follow the alternating pattern.

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By reviewing and adjusting the conversation input to clearly alternate between the user and assistant roles—and verifying that binary data is not interfering with this structure—you should be able to resolve the error with the Amazon Bedrock Chat model in your updated n8n instance.

Let me know if you need further assistance!