presta shop product features are not getting added through webservice

Question

Am trying to add a product to prestashop through web service.Am able to add everything but the product feature value is not getting added. The feature label is getting selected in backend but the value is empty. The product xml is given below

<?xml version="1.0" encoding="UTF-8"?>
<prestashop xmlns:xlink="http://www.w3.org/1999/xlink">
<product>
    <id></id>
    <id_manufacturer>1</id_manufacturer>
    <id_supplier>1</id_supplier>
    <id_category_default>5</id_category_default>
    <new>1</new>
    <cache_default_attribute>1</cache_default_attribute>
    <id_default_image>1</id_default_image>
    <id_default_combination>1</id_default_combination>
    <id_tax_rules_group>1</id_tax_rules_group>
    <position_in_category>0</position_in_category>
    <type>simple</type>
    <id_shop_default>1</id_shop_default>
    <reference>demo_1</reference>
    <supplier_reference></supplier_reference>
    <location></location>
    <width>0.000000</width>
    <height>0.000000</height>
    <depth>0.000000</depth>
    <weight>0.000000</weight>
    <quantity_discount>0</quantity_discount>
    <ean13>0</ean13>
    <isbn></isbn>
    <upc></upc>
    <cache_is_pack>0</cache_is_pack>
    <cache_has_attachments>0</cache_has_attachments>
    <is_virtual>0</is_virtual>
    <state>1</state>
    <on_sale>0</on_sale>
    <online_only>0</online_only>
    <ecotax>0.000000</ecotax>
    <minimal_quantity>1</minimal_quantity>
    <price>12.00</price>
    <wholesale_price>10.00</wholesale_price>
    <unity></unity>
    <unit_price_ratio>0.000000</unit_price_ratio>
    <additional_shipping_cost>0</additional_shipping_cost>
    <customizable>0</customizable>
    <text_fields>0</text_fields>
    <uploadable_files>0</uploadable_files>
    <active>1</active>
    <redirect_type>404</redirect_type>
    <id_type_redirected>0</id_type_redirected>
    <available_for_order>1</available_for_order>
    <available_date>0000-00-00</available_date>
    <show_condition>0</show_condition>
    <condition>new</condition>
    <show_price>1</show_price>
    <indexed>1</indexed>
    <visibility>both</visibility>
    <advanced_stock_management>0</advanced_stock_management>
    <date_add></date_add>
    <date_upd></date_upd>
    <pack_stock_type>3</pack_stock_type>
    <meta_description><language id="1">dsgfdsgdf</language></meta_description>
    <meta_keywords><language id="1">fgdgdfgdf</language></meta_keywords>
    <meta_title><language id="1">dfgdfgdf</language></meta_title>
    <link_rewrite><language id="1"></language></link_rewrite>
    <name><language id="1">New Product</language></name>
    <description><language id="1">kk descritption</language></description>
    <description_short><language id="1">kk</language></description_short>
    <available_now><language id="1"></language></available_now>
    <available_later><language id="1"></language></available_later>
<associations>
<categories>
    <category>
    <id>2</id>
    </category>
</categories>
<images>
    <image>
    <id></id>
    </image>
</images>
<combinations>
    <combination>
    <id></id>
    </combination>
</combinations>
<product_option_values>
    <product_option_value>
    <id></id>
    </product_option_value>
</product_option_values>
<product_features>
    <product_feature>
        <id>8</id>
        <custom>1</custom>  
        <id_feature_value>222</id_feature_value>
    </product_feature>
</product_features>
<tags>
    <tag>
    <id></id>
    </tag>
</tags>
<stock_availables>
    <stock_available>
    <id>1</id>
    <id_product_attribute>0</id_product_attribute>
    </stock_available>
</stock_availables>
<accessories>
    <product>
    <id></id>
    </product>
</accessories>
<product_bundle>
    <product>
    <id></id>
    <quantity></quantity>
    </product>
</product_bundle>
</associations>
</product>
</prestashop>

below given the feature part of the xml

<product_features>
    <product_feature>
        <id>8</id>
        <custom>1</custom>  
        <id_feature_value>222</id_feature_value>
    </product_feature>
</product_features>

attaching the backend screen.