C# ASP.Net Core how to return Json() response from an api controller

Question

I currently have an asp.net core 2.2 webapi api controller. Returning Ok result with the response. But the requirement is to return Json() response.

    [HttpGet]
    [Route("employee/{employeeId}")]
    public async Task<IActionResult> GetUserFromEmployeeNumber(string employeeId)
    {
        var correlationId = _correlationContextAccessor.CorrelationContext.CorrelationId;

        try
        {
            var response = await _service.GetUserByEmployeeId(employeeId);
            return Ok(response); //How to return Json().
        }
        catch (Exception exception)
        {
            return BadRequest(message);
        }
    }

For above, i get 204 No Content response if response is null.

Do i need to any reference package to use Json()? If so what is the correct package reference?

Thanks