如何将JSON数据解码为php，而数据格式就像{“1”：Data1，“2nd”：Data2}

I want to decode this data into a php obj, but this is not working. If I run the code it gives nothing.

$Data = "{"3":false,"5":false,"6":true}" 

$obj = json_decode($Data, true);
echo $obj["3"];
echo $obj["5"];

Look at the below code.

$ch = curl_init();

curl_setopt($ch, CURLOPT_URL, "https://demo.thingsboard.io:443/api/plugins/rpc/twoway/67cadda0-b8c0-11e8-a04e-eb5f6cd0fada");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, "{\"method\": \"setGpioStatus\", \"params\": {\"pin\": \"".$PIN_NUMBER."\", \"enabled\": \"".$PIN_STATUS."\"}, \"timeout\": \"500\"}");
curl_setopt($ch, CURLOPT_POST, 1);

$headers = array();
$headers[] = "Content-Type: application/json";
$headers[] = "Accept: */*";
$headers[] = "X-Authorization: Bearer ".$New_JWT_TOKEN."";
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

$GPIO_RESULT = curl_exec($ch); // curl_exec($ch) gives {"3":false,"5":false,"6":true}
if (curl_errno($ch)) {
    echo 'Error:' . curl_error($ch);
}
curl_close ($ch);

$obj = json_decode($GPIO_RESULT, true);
echo $obj["3"]; // output: null 

echo $GPIO_RESULT;  // output: {"3":false,"5":false,"6":true}
}

Now I get the output of $GPIO_RESULT but not the output of $obj["3"] or any single digit integer. I found that no integer value is accepted at this format. Can anyone tell me any other way to converting this data.