HUGGINGFACE ValidationError: 1 validation error for StuffDocumentsChain __root__

Question

I am getting this error ValidationError: 1 validation error for StuffDocumentsChain root document_variable_name context was not found in llm_chain input_variables: ['chat_history', 'user_query', 'relevant_context'] (type=value_error) while using load_qa_chain I have searched this error but did n't find anything related to this. Can anyone tell what I am missing here.

I dont know if HuggingFaceEndpoint is the correct. It suppose I'm replacing an OpenIA code with a Huggingface one and it running in the huggingface workspce as an app.

I'm using Huggingface and this is the code:

def chat_engine():
    retriever = PDF_KnowledgeBase('./KnowledgeBase').return_retriever_from_persistant_vector_db()
    huggingface_hub = HuggingFaceEndpoint(
        endpoint_url="http://localhost:8010/",
        max_new_tokens=512,
        top_k=10,
        top_p=0.95,
        typical_p=0.95,
        temperature=0.01,
        repetition_penalty=1.03,
        huggingfacehub_api_token="mytoken"
    )
    
    template = """
        <template content>
        """
    PROMPT = PromptTemplate(template=template, input_variables=['question'])

    document_variable_name = "context"

    # Set up question-answering chain
    qa_chain = RetrievalQA.from_chain_type(
        llm=huggingface_hub,
        chain_type='stuff',
        retriever=retriever,
        chain_type_kwargs={"prompt": PROMPT},
        return_source_documents=False
    )

    return qa_chain

I tried changing all the parameters without success