CreateBook.cs

 [FunctionName(nameof(CreateBook))]
        public async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.Anonymous, "post", Route = "CreateBook")] HttpRequest req)
        {
            IActionResult returnValue = null;

            string requestBody = await new StreamReader(req.Body).ReadToEndAsync();

            var input = JsonConvert.DeserializeObject<BookModel>(requestBody);

            var book = new BookModel
            {
                Title= input.Title,
                Author=input.Author,
                Publisher=input.Publisher,
                Category= input.Category, 
                Price = input.Price,
                PublishDate = input.PublishDate 
            };

            try
            {
                _books.InsertOne(book);
                returnValue = new OkObjectResult(book);
            }
            catch (Exception ex)
            {
                _logger.LogError($"Exception thrown: {ex.Message}");
                returnValue = new StatusCodeResult(StatusCodes.Status500InternalServerError);
            }
            return returnValue;
        }