{"message":"invalid json"}

$json = '{
"sex": "'.$gender.'",
"age": '.$age.',
"evidence": [
{"id": "'.$symptom_id1.'", "choice_id": "present", "initial": true},
{"id": "'.$symptom_id2.'", "choice_id": "present", "initial": true},
{"id": "p_7", "choice_id": "'.$test1.'"},
{"id": "p_8", "choice_id": "'.$test2.'"},
{"id": "p_9", "choice_id": "'.$test3.'"},
{"id": "p_10", "choice_id": "'.$test4.'"},
{"id": "p_28", "choice_id": "'.$test5.'"},
{"id": "'.$location.'", "choice_id": "present"}
],
"extras": {
"disable_groups": true
}
}';
$ch = curl_init('https://api.infermedica.com/v2/diagnosis');
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_POSTFIELDS, $json);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
curl_setopt($ch, CURLOPT_HTTPHEADER, [
'Content-Type: application/json',
'Content-Length: ' . strlen($json),
'app_id: '. APP_ID,
'app_key: '. APP_KEY,
'Interview-Id: '.$interview_id,
'User-Id: '. $hasheduser_id
]);
$result = curl_exec($ch);

echo '<pre>';
print_r( $result );
echo '</pre>';