我正在尝试将petfinder APi用于正在创建的应用程序，并遵循可以在以下网址找到的API文档：https://www.petfinder.com/developers/v2/docs/#developer-resources。

它给出命令：curl -d "grant_type=client_credentials&client_id={CLIENT-ID}&client_secret={CLIENT-SECRET}" https://api.petfinder.com/v2/oauth2/token

我正在尝试将其翻译为React native，并使用了以下代码：

getadopt1 = async() => {
fetch('https://api.petfinder.com/v2/oauth2/token',{
method: 'POST',headers: {
accept: 'application/json','Content-Type': 'application/json',},body: JSON.stringify({
firstParam: "grant_type=client_credentials&client_id={CLIENT-ID}&client_secret={CLIENT-SECRET}"
}),}).then((response) => response.json())
.then((responseJson) => {
let res = JSON.stringify(responseJson)
console.log("Response: "+res)
return responseJson;
})
.catch((error) => {
console.error(error);
})
}

但是我遇到以下错误：

Response: {"type":"https://httpstatus.es/400","status":400,"title":"unsupported_grant_type","detail":"The authorization grant type is not supported by the authorization server.","errors":[{"code":"unsupported_grant_type","title":"Unauthorized","message":"The authorization grant type is not supported by the authorization server. - Check that all required parameters have been provided","details":"The authorization grant type is not supported by the authorization server. - Check that all required parameters have been provided","href":"http://developer.petfinder.com/v2/errors.html#unsupported_grant_type"}],"hint":"Check that all required parameters have been provided"}

我在这里做什么错了？