Request fails on curl but works on guzzle - php

Question

Am using the following post request on guzzle to microsoft graph which works.
$client = new Client([
'headers' => [ 'Content-Type' => 'application/json', 'Authorization' => 'Bearer ' . $token ]
]);
$url = "myurl";
$response = $client->post(
$url,
[
'body' => json_encode(
[
"startDateTime"=>$arr['start_date'],
"endDateTime"=>$arr['end_date'],
"meeting"=>$arr['subject']
]
)]
);
$payload = json_decode($response->getBody()->getContents());
var_dump($payload) //here has data
The am doing the same request via curl using
$post = [
"meeting"=>$arr['subject'],
"startDateTime"=>$arr['start_date'],
"endDateTime"=>$arr['end_date'],
];
$authorization = "Authorization: Bearer ".$token;
$headers = [
'Content-Type' => 'application/json',
$authorization
];
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($post));
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
$response = curl_exec($ch);
$error = curl_errno($ch) ? curl_error($ch) : '';
curl_close($ch);
if ($error){
var_dump($error);
throw new Exception($error,500);
}
return $response;
But in curl the above in micorsoft graph throws an error Expected not null\r\nParameter name: meeting but the meeting parameter is not empty. I have also tried setting the value of meeting directly via
$post = [
"meeting"=>"Test meeting",
"startDateTime"=>$arr['start_date'],
"endDateTime"=>$arr['end_date'],
];
But still doesnt solve. I guess it has something to do with body parameter i have set on guzzle which works. How can i resolve this to have it work even on curl