Fetch POST returns HTTP 415 while curl goes fine and returns the result

This is how my code looks like

let body = {
            authCode: "XXXX",
            clientId: "YYYYYY",
            clientSecret: "ZZZZZZ"
        };


        fetch('https://api.myapp.com/oauth/token',{
            method: "POST",
            headers: {
                "Content-Type": "application/json",
                "Accept": "application/json"
            },
            mode: 'no-cors',
            body: body
        }).then(function(response){
            console.log("response: ", response);
        }).catch(function(error){
            console.log("could not get tokens: ", error);
        })

      

        
        
        
      

    

In Chrome this is what I see

I tried to do it with curl command

and it looks like this:

➜  ~ curl -X POST -H "Content-Type: application/json" -d '{
  "authCode": "XXXX",
  "clientId": "YYYYY",
  "clientSecret": "ZZZZZZZZ"
}' https://api.myapp.com/oauth/token
{"authToken":"e141kjhkwr3432ca9b3d2128385ad91db4cd2:cca6b151-cab4-4de2-81db-9a739a62ae88:23000000"}

      

        
        
        
      

    

What am I doing wrong here?

UPDATE

After you changed it to the following, the result is still HTTP 415

fetch('https://api.myapp.com/oauth/token',{
            method: "POST",
            headers: {
                "Content-Type": "application/json",
                "Accept": "application/json"
            },
            mode: 'no-cors',
            body: JSON.stringify(body)
        }).then(function(response){
            console.log("response: ", response);
        }).catch(function(error){
            console.log("could not get tokens: ", error);
        })

      

        
        
        
      

    

I wonder if I figured out I sent the header "Content-Type": "application/json"

while I get back content-type: text/plain

, why might this be happening?