Exposing Azure Funtion as MCP Server in Azure API Manager is not passing POST body to API

When I expose my Azure Function as an MCP server through API Management, I find that the expected body doesn’t reach my Azure Function. I get the following error:

“An error has occurred with Inputs args: Expecting value: line 1 column 1 (char 0)”

@app.route(route="search_documents",  methods=["POST"])
def search_documents(req: func.HttpRequest) -> func.HttpResponse:
    """
    List metadata details of documents stored in a specific SharePoint folder.

    Args:
       context: The trigger context containing the input arguments.

    Returns:
        A dictionary containing the metadata for each document, exported in JSON format.
    """

    try:
        # input args
        inputs = loads(req.get_body())

        site_url = inputs["site_url"]
        folder_path = inputs["folder_path"]
        user_email = inputs["user_email"]
        document_library = inputs["document_library"]

        logger.info("Info: Input arguments have been loaded into the Metadata tool function.")
    except Exception as e:
        logger.error(f"Metadata tool An error has occurred with Inputs args: {e}")
        return func.HttpResponse(dumps({"error":"Metadata tool: An error has occurred with the input arguments. Please validate that they are not empty and are the correct data type."}), status_code=400, mimetype="application/json")

If I add the following policy to each endpoint in API Management, the MCP starts working correctly. However, I notice that performance worsens — for queries that return a lot of information, using the Azure Function directly works fine without reaching a timeout, but when using it through MCP, the requests get stuck:

<policies>
    <inbound>
        <base />
        <!-- Guardar el body original para depuración -->
        <set-variable name="originalBody" value="@{
            return context.Request.Body.As<string>(preserveContent: true);
        }" />
        <!-- Enviar el mismo body original al backend -->
        <set-body>@(context.Variables.GetValueOrDefault<string>("originalBody"))</set-body>
        <set-backend-service id="apim-generated-policy" backend-id="myaftest" />
    </inbound>
    <backend>
        <base />
    </backend>
    <outbound>
        <base />
    </outbound>
    <on-error>
        <base />
    </on-error>
</policies>																									

I’m experiencing issues similar to those in this post: Exposing API as MCP Server in Azure API Manager is not passing POST body to API, but I don’t see that anyone has provided an answer.