httpClient.PutAsync() not updating, 415 Unsupported media type

Question

I am building a Rest API and a Rest Client , the api url is https://localhost:44341 and the client url is https://localhost:44305/ , specifically I want to be able to edit pages in the client for a small custom cms.

Anyway, to view a page in the client, I do this:

public async Task<IActionResult> Edit(long id)
{
    Page page = new Page();
    using (var httpClient = new HttpClient())
    {
        using var response = await httpClient.GetAsync("https://localhost:44341/api/Pages/" + id);
        string apiResponse = await response.Content.ReadAsStringAsync();
        page = JsonConvert.DeserializeObject<Page>(apiResponse);
    }
    return View(page);
}

And it works, I get the actual page data from the API, however the PUT method in the client is not working, this is it:

[HttpPost]
public async Task<IActionResult> Edit(Page page)
{
    using (var httpClient = new HttpClient())
    {
        using var response = await httpClient.PutAsync("https://localhost:44341/api/Pages/" + 
              page.Id, new StringContent(page.ToString()));

        string apiResponse = await response.Content.ReadAsStringAsync();
    }

    return Redirect(Request.Headers["Referer"].ToString());
}

When I submit the form for the above method it just redirects to the previous request but the changes aren't saved.

Here's the put method from the api:

[HttpPut("{id}")]
public async Task<ActionResult> PutPage(long id, Page page)
{
    if (id != page.Id)
    {
        return BadRequest();
    }

    context.Entry(page).State = EntityState.Modified;
    await context.SaveChangesAsync();

    return NoContent();
}

When I inspect using breakpoints, I can see that the response in the POST method says 415 unsupported media type

Answer 1

The 415 unsupported media type status code means that

The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method.

When you use new StringContent(page.ToString()) then the media type for the StringContent created defaults to text/plain.

You need to send content in json format:

var content = new StringContent(JsonConvert.SerializeObject(page, Encoding.UTF8, "application/json");   
using var response = await httpClient.PutAsync($"https://localhost:44341/api/Pages/{page.Id}", content);