GetSellerList Returning My Own Items With Another Userid Specified

So I'm seeing some unusual activity with the Trading API using the GetSellerList action. Making any call while I'm specifying ANY value results in me returning only my ebay items. I'm looking at pulling another users sellerslist, not my own. I've tried multiple API versions, but my script is using 871.

<?php

function print_d($array){    echo "<pre>\n";    print_r($array);    echo "</pre>\n";}

$mytoken = "*************mytoken ****************";
$devId = "**************devId ***************";
$appId = "*************appId ***************";
$certId = "**************certId **************";

$wsdl_url = 'http://developer.ebay.com/webservices/latest/ebaySvc.wsdl';

$apiCall = "GetSellerList";

$credentials = array('AppId' => $appId, 'DevID' => $devId, 'AuthCert' => $certId);

$client = new SOAPClient($wsdl_url, array('trace' => 1, 'exceptions' => 0, 'location' => "https://api.ebay.com/wsapi?callname=$apiCall&appid=$appId&siteid=0&version=871&Routing=new"));

$eBayAuth = array('eBayAuthToken' => new SoapVar($mytoken, XSD_STRING, NULL, NULL, NULL, 'urn:ebay:apis:eBLBaseComponents'),
                    'Credentials' => new SoapVar ($credentials, SOAP_ENC_OBJECT, NULL, NULL, NULL, 'urn:ebay:apis:eBLBaseComponents'));  

$header_body = new SoapVar($eBayAuth, SOAP_ENC_OBJECT);    

$header = array(new SOAPHeader('urn:ebay:apis:eBLBaseComponents', 'RequesterCredentials', $header_body));                

//set the API call parameters

$params = array('UserID'=>'**userid**','DetailLevel'=>'ReturnAll','GranularityLevel'=>'Coarse','WarningLevel'=>'High','IncludeWatchCount'=>'true','Pagination'=>array('EntriesPerPage'=>20,'PageNumber'=>1),'Version' => 871, 'StartTimeFrom'=>'2019-07-01T01:01:02.768Z' ,'StartTimeTo'=>'2019-08-22T01:01:02.768Z');  

$request = $client->__soapCall($apiCall, array($params), NULL, $header);  //make the actual API call

print_d($request);



?>