Consultar cliente API ASAAS

getCustomer.php

$ch = curl_init(); 
curl_setopt($ch , CURLOPT_URL, "https://www.asaas.com/api/v3/customers");
curl_setopt($ch , CURLOPT_HTTPGET, true);
curl_setopt($ch , CURLOPT_RETURNTRANSFER, true);                                                                      
curl_setopt($ch , CURLOPT_HTTPHEADER, array(                                                                          
    "Content-Type: application/json",                                                
    "access_token: <COLOQUE AQUI A SUA API>"
    )); 
$response = curl_exec($ch);
curl_close($ch);

var_dump($response);