//initiliaze php curl 
$curl = curl_init();
curl_setopt_array($curl, array(
    CURLOPT_URL => "https://api.backlinkseo.com/v1.2/domains/",
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_ENCODING => "",
    CURLOPT_MAXREDIRS => 10,
    CURLOPT_TIMEOUT => 30,
    CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
    CURLOPT_CUSTOMREQUEST => "GET",
    CURLOPT_HTTPHEADER => array(
        "content-type: application/x-www-form-urlencoded",
        "token: [YOUR API KEY]"
    )
));
$result = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);

$getResponse = json_decode($result);
print_r($getResponse);

//initiliaze php curl 
$curl = curl_init();
curl_setopt_array($curl, array(
    CURLOPT_URL => "https://api.backlinkseo.com/v1.2/backlinks/?domainId=[DOMAIN ID]",
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_ENCODING => "",
    CURLOPT_MAXREDIRS => 10,
    CURLOPT_TIMEOUT => 30,
    CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
    CURLOPT_CUSTOMREQUEST => "GET",
    CURLOPT_HTTPHEADER => array(
        "content-type: application/x-www-form-urlencoded",
        "token: [YOUR API KEY]"
    )
));
$result = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);

$getResponse = json_decode($result);
print_r($getResponse);

Notes :
sortOrder Options :  accending/decending
sortBy Options : activelinks/inactivelinks/dofollow/nofollow/sponsored/mozDA/mozPA/mozRank/majesticCF/majesticTF