Schema validation error when using Restriction in EWS FindItem request - soap

Question

I'm trying to find items in inbox with ItemClass = IPM.Note
<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:tns="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:wsi="http://ws-i.org/schemas/conformanceClaim/">
<soap:Header>
<t:RequestServerVersion Version="Exchange2010_SP2"></t:RequestServerVersion>
</soap:Header>
<soap:Body>
<FindItem Traversal="Shallow" xmlns="http://schemas.microsoft.com/exchange/services/2006/messages">
<ItemShape>
<t:BaseShape xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types">IdOnly</t:BaseShape>
<t:AdditionalProperties xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types">
<t:FieldURI FieldURI="item:ItemClass"></t:FieldURI>
</t:AdditionalProperties>
</ItemShape>
<IndexedPageItemView MaxEntriesReturned="50" Offset="0" BasePoint="Beginning"></IndexedPageItemView>
<Restriction>
<IsEqualTo>
<FieldURI FieldURI="item:ItemClass"></FieldURI>
<FieldURIOrConstant>
<Constant Value="IPM.Note"></Constant>
</FieldURIOrConstant>
</IsEqualTo>
</Restriction>
<ParentFolderIds>
<t:DistinguishedFolderId Id="inbox" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types"></t:DistinguishedFolderId>
</ParentFolderIds>
</FindItem>
</soap:Body>
</soap:Envelope>
Resulting in this SchemaValidationError
a:ErrorSchemaValidation: The request failed schema validation: The element 'Restriction' in namespace 'http://schemas.microsoft.com/exchange/services/2006/messages' has invalid child element 'IsEqualTo' in namespace 'http://schemas.microsoft.com/exchange/services/2006/messages'. List of possible elements expected: 'SearchExpression' in namespace 'http://schemas.microsoft.com/exchange/services/2006/types'. [undefined] Error: a:ErrorSchemaValidation: The request failed schema validation: The element 'Restriction' in namespace 'http://schemas.microsoft.com/exchange/services/2006/messages' has invalid child element 'IsEqualTo' in namespace 'http://schemas.microsoft.com/exchange/services/2006/messages'. List of possible elements expected: 'SearchExpression' in namespace 'http://schemas.microsoft.com/exchange/services/2006/types'.
To my understaning, SearchExpression is an abstract type that can be replaced with IsEqualTo, among other types.
What am I missing here?

Answer 1

Some of these elements are in the 'types' namespace so they need the t: prefix
<Restriction>
<t:IsEqualTo>
<t:FieldURI FieldURI="item:ItemClass"></t:FieldURI>
<t:FieldURIOrConstant>
<t:Constant Value="IPM.Note"></t:Constant>
</t:FieldURIOrConstant>
</t:IsEqualTo>
</Restriction>