Using Extension Attribute for OrderBy element in an API Call

Answer

Extended attributes have to be part of Extn element. Else they cannot be accessed. So, in this case, inside Orderby element, you need an Extn element and inside that you need Attribute element.

Please find below a sample input xml with various kinds of OrderBy clauses
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<Page  PageSize="10" PaginationStrategy="NEXTPAGE">
    <API Name="getItemListForOrdering">
        <Input>
            <Item CallingOrganizationCode="DEFAULT"
IgnoreInvalidItems="N" InheritAttributesFromClassification="Y"
ItemGroupCode="PROD" ItemIDQryType="FLIKE">
                <ItemAttributeGroupTypeList>
                    <ItemAttributeGroupType
ClassificationPurposeCode="DISPLAY_ATTRIBUTES"/>
                </ItemAttributeGroupTypeList>
                <OrderBy>
                    <Attribute Desc="Y" Name="ShortDescription"/>
                    <Attribute Desc="Y" Name="Description"/>
                     <Extn>
                    <Attribute Desc="Y" Name="ExtnReturnPolicy"/>
                     </Extn>
                </OrderBy>
            </Item>
        </Input>
    <Template>
            <ItemList TotalItemList="" TotalNumberOfRecords="">
                <Item CanUseAsServiceTool="" GlobalItemID=""
InheritAttributesFromClassification="" IsItemSuperseded=""
ItemGroupCode="" ItemID="" ItemKey="" MaxModifyTS=""
OrganizationCode="Required" SubCatalogOrganizationCode=""
UnitOfMeasure="">
                    <Extn/>
                    <PrimaryInformation Description=""
ShortDescription=""/>
                </Item>
            </ItemList>
        </Template>
    </API>
</Page>
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