The completion operation does not work with the specified model, gpt-4

I have this LangChain code for answering questions by getting similar docs from the vector store and using llm to get the answer of the query:

llm_4 = AzureOpenAI(
        # temperature=0,
        api_version= os.environ['OPENAI_API_VERSION_4'], 
        openai_api_key= os.environ['AZURE_OPENAI_API_KEY_4'], 

        deployment_name="gpt4-deploy",
        # model_name="gpt4-o",
        azure_endpoint=os.environ['AZURE_OPENAI_ENDPOINT_4']
    )

    llm_3 = AzureOpenAI(
        # temperature=0,
        api_version= os.environ['OPENAI_API_VERSION_3'], 
        openai_api_key= os.environ['AZURE_OPENAI_API_KEY_3'], 

        deployment_name="test-deployment", 
        # deployment_name="gpt-16k-deployment",
        # model_name="gpt-3.5-turbo-16k",

        azure_endpoint=os.environ['AZURE_OPENAI_ENDPOINT_3']
    )

    response=get_answer(relavant_docs, user_input, llm_4)

...

#Create embeddings instance
def create_embeddings():
    #embeddings = OpenAIEmbeddings()
    embeddings = SentenceTransformerEmbeddings(model_name="all-MiniLM-L6-v2")
    # embeddings = SentenceTransformerEmbeddings(model_name="text-davinci-003") 
    return embeddings


def get_answer(docs, user_input, llm=None):
    if llm:
        chain = load_qa_chain(llm, chain_type="stuff")
    else:
        chain = load_qa_chain(OpenAI(), chain_type="stuff")

    with get_openai_callback() as cb:
        response = chain.run(input_documents=docs, question=user_input)
    return response

It's working with gpt3, but with gpt4 getting:

BadRequestError: Error code: 400 - {'error': {'code': 'OperationNotSupported', 'message': 'The completion operation does not work with the specified model, gpt-4. Please choose different model and try again. You can learn more about which models can be used with each operation here: https://go.microsoft.com/fwlink/?linkid=2197993.'}}

I tried what was suggested by these similar issues:

How to use the new gpt-3.5-16k model with langchain?

I am trying to make a docs question answering program with AzureOpenAI and Langchain

But I still didn't figure out how to solve it!

Just giving it has an answer. So, that it helps community to find better solution.

Internally, the chain invokes the completion Api to the model which it is not supported and gives you the error.

In such case you can either use supported model or azure OpenAI chat client AzureChatOpenAI.

To see which model are supported for completions operation, in the model tab you check mark Completion and save.

As you can see the instruct model are supported.