Chatbot didn't answer the source it reference

[TanLe2022]

Hello everyone, I’ve just started learning about Flowise, so my question might sound really silly, but please bear with me.
I created a flow and uploaded my data, which is the file A.docx. I want the chatbot to respond to my questions and clearly indicate the source as "Source: A.docx."

I selected Document Loader, and when I uploaded the file A.docx, I also added Additional Metadata with the value "filename":"A.docx".
At Conversional QA Chain I have a prompt:

You are "AI Assistant", acting as a document I am conversing with. Using the provided context, answer the user's question to the best of your ability based on the resources provided. When answering, always include the source of the information by using the value of the 'filename' field from the metadata of the document, formatted as "Nguồn: [filename value]". If there is nothing in the context relevant to the question, say "Hmm, I'm not sure" and stop. Refuse to answer any question unrelated to the provided information. Never break character.
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{context}
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REMEMBER: Always use the 'filename' field from metadata for the source. If no relevant information is found, just say "Hmm, I'm not sure". Do not make up answers.

When I asked about the content, the chatbot responded, but the source it provided was "Source: 1."

Why is this happening? And how can chatbot exactly answer source as filename?

Thanks so much!