Legacy API key migration - PHP ISDK

this code of ine already have the SAK key assigned

\PhpXmlRpc\Client::OPT_CUSTOM_HEADER => array('X-Keap-API-Key: ’ . $this->key),

can you tell me where exactly I will have to perform the 3rd step

  1. Pass the SAK in the custom header: X-Keap-Api-Key: {SAK_GOES_HERE}

hopefully this will resolve my issue

Im geeting this error now

Fatal error : Uncaught iSDKException: No connection information found. in /home/kayadeve/public_html/farrukh/isdk.php:59 Stack trace: #0 /home/kayadeve/public_html/farrukh/index.php(7): iSDK->cfgCon(‘ISCON’) #1 {main} thrown in /home/kayadeve/public_html/farrukh/isdk.php on line 59