' => "MY_SELLER_ID",     'FeedType' => "_POST_PRODUCT_DATA_",     'SignatureMethod' => "HmacSHA000",     'SignatureVersion' => "0",     'Timestamp'=> $timestamp,     'Version'=> "0000-00-00",     'MarketplaceIdList.Id.0' => "MY_MARKETPLACE_ID",     'PurgeAndReplace'=>'false' );  $secret = 'MY_SECRET_KEY'; 