Using dotnet 8, Asp.net Core api, I tried setting up a simple toy example of an API server with some endpoints. Client side, it’s a simple React app that queries the endpoints with a fetch request. I don’t understand why, but POST/PUT/PATCH endpoints whose methods take input are not getting the data in the request body. It’s coming in as null. My example code is below.

I don’t have this issue with GET endpoints where the associated methods have inputs. If I change the input type to dynamic instead of string, then it is able receive the request body.

What I tried:
Server endpoint example:

[HttpPost]
[Route("simplesubmit")]
public void SimpleSubmit([FromBody] string dataAsString){
   // simple work
}

Client fetch example:

await fetch ("urlgoeshere.com/simplesubmit", {
   method: "POST",
   headers: {
      "Content-Type": "application/json"
   },
   body: JSON.stringify({
      name: "my name"
   })
});

What happens:
The SimpleSubmit method isn’t called, and there’s a network response of 400 indicating that the dataAsString field is required.