How to provide a nested SObject for foreign key field - php

Question

I am trying to create a new opportunity from USSD App in salesforce via php rest api. I am parsing the record Type id instead of the record type name. Below is the Snippet for creating new opportunity.
public function log_case_opp( $sobject = 'Opportunity', $recordType = '012D00000003H8DIAU', $name='XXXXXX', $account, $stage, $currency='KES - Kenyan Shilling', $close_date ) {
$url = "$this->instance_url/services/data/v24.0/sobjects/{$sobject}/";
$content = json_encode(array("Name" => "{$name}",
"RecordType" => "{$recordType}",
"Account" => "{$account}",
"StageName" => "{$stage}",
"CurrencyIsoCode" => "{$currency}",
"CloseDate" => "{$close_date}"
));
$curl = curl_init($url);
curl_setopt($curl, CURLOPT_HEADER, false);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_HTTPHEADER,
array("Authorization: OAuth $this->access_token",
"Content-type: application/json"));
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_POSTFIELDS, $content);
$json_response = curl_exec($curl);
$status = curl_getinfo($curl, CURLINFO_HTTP_CODE);
if ($status == 400 && $json_response['error_description'] == 'expired authorization code') {
//access code has been expired
die('ERROR : new code required');
}elseif ( $status != 201 ) {
die("Error: call to URL $url failed with status $status, response $json_response, curl_error " . curl_error($curl) . ", curl_errno " . curl_errno($curl));
}
curl_close($curl);
$response = json_decode($json_response, true);
return $response["id"];
}
When trying to create the opportunity am getting the error below
[{"message":"The value provided for foreign key reference RecordType is not a nested SObject","errorCode":"INVALID_FIELD"}]
Please help on what am doing wrong or not doing

Answer 1

i have been able to solve this error by adding Id to the reference fields i.e. changing the $content code block to :
$content = json_encode(array("Name" => "{$name}",
"RecordTypeId" => "{$recordType}",
"AccountId" => "{$account}",
"StageName" => "{$stage}",
"CurrencyIsoCode" => "{$currency}",
"CloseDate" => "{$close_date}"
));