.Net Core C# Rest API "Method Not Allowed"

Question

I have a .Net Core C# API that looks like this:

    [HttpPut]
    [Route("{primaryKey}")]
    public async Task<ActionResult<ResponseSingleX<ClassA>>> Update(Guid primaryKey, ClassA classA)
    {
        // Update database
    }

I try to do an update using the following code:

// Create a ClassA object and put some data in it
...

//GetServiceUrl() == return "http://localhost:9003/api/Configurations/";
serviceUrl = _shared.GetServiceUrl() + classA.PrimaryKey.ToString();
string requestBody = System.Text.Json.JsonSerializer.Serialize(classA);
HttpContent requestContent = new StringContent(requestBody, Encoding.UTF8, "application/json");
HttpResponseMessage responseMessage = await client.PutAsync(serviceUrl, requestContent);
Stream responseStream = await responseMessage.Content.ReadAsStreamAsync();
responseMessage.EnsureSuccessStatusCode();
var updatedResponse = await System.Text.Json.JsonSerializer.DeserializeAsync<ResponseSingleX<ClassA>>(responseStream, _serializerOptions);
Assert.True(updatedResponse.Success);
var updatedClassA = updatedResponse.Element;

The problem I have is that responseMessage == "Method Not Allowed". Since this is literarily the first time I have ever used Rest (no matter the programming language), I am at a loss to why this does not work.

UPDATE 0: I found my mistake. See my answer for the cause of the problem. Thank you for your help!

Answer 1

I found my error. The class itself has an URL defined that defines additional parameters.

[Route("...") // <-This is what I missed
[ApiController]
public class SomeController
{
    ...
}

Answer 2

Try adding [FromBody] attribute before ClassA:

[HttpPut]
[Route("{primaryKey}")]
public async Task<ActionResult<ResponseSingleX<ClassA>>> Update(Guid primaryKey, [FromBody] ClassA classA)
{
    // Update database
}