Buat Variabel di PHP Curl

Assalamualaikum,.. cukup tulis tanpa kutip satu atau dua,  
jadi seperti ini : "sender":$username,

atau begini harusnya juga bisa : "sender":"$username",

Waalaikumsalam. 
 
"sender":"'. $username.'",

Assalamualaikum,.. 
 
Klo boleh saran.. lebih baik disimpan didalam array lalu convert ke json menggunakan json_encode untuk postfields-nya.
 
$curl = curl_init();
$username = "dingtangtong"
$postfields = array(
	'sender'	=> $username,
	'token'		=> 'zbequwdio456',
	'type'		=> 'image',
	'number'	=> '628113004277',
	'message'	=> 'Tess Kirim WA by API',
	'url'		=> 'http://wa.domain.id/img/brosur.jpg'
);
curl_setopt_array($curl, array(
  CURLOPT_URL => 'http://wa.domain.id/apiv1/sendText',
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => '',
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 0,
  CURLOPT_FOLLOWLOCATION => true,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => 'GET',
  CURLOPT_POSTFIELDS => json_encode($postfields),
  CURLOPT_HTTPHEADER => array(
    'Content-Type: application/json'
  ),
));
 
$response = curl_exec($curl);
 
curl_close($curl);
echo $response;