Base64 payload and XML to objects

I am trying to import a large base64 string into objects but I can't seem to get it to work:

ClassMethod Test() As %Status
{
Set readerForItkRequestData = ##class(%XML.Reader).%New()
 
Set file="c:\Source\test_full.xml"
 
Set status = readerForItkRequestData.OpenFile(file)
Do readerForItkRequestData.Correlate("Envelope","Phu.Epro.Schema.Itk.Envelope")
set temp = readerForItkRequestData.Next(.pOutput,.tStatus)
Do pOutput.%Save()

}

The class I'm trying to project to: 

Class Phu.Epro.Schema.Itk.Payload Extends (%Persistent, %XML.Adaptor)
{

Parameter XMLIGNOREINVALIDTAG = 1;

Property ManifestItemId As %String(XMLNAME = "id", XMLPROJECTION = "attribute");

Property FileName As %String(XMLNAME = "filename", XMLPROJECTION = "attribute");

Property Test As %String(MAXLEN = "", XMLPROJECTION = "content");}

The error I get is:

Datatype validation failed for tag, payload (ending at line 40 character 36), with value:

Here's the xml trying to be imported, with the base64 stripped:

<payload filename="eaf7a956-f09e-43a0-9a20-95696dc5acac.pdf" id="binaryDocument">J....YNCg==</payload>

It's worth mentioning this is a collection. The Payloads can also be quite different (notice how the first one doesn't have "content" and is complex type:

<payload id="clinicalDocument">
    <ClinicalDocument xmlns="urn:hl7-org:v3" xmlns:npfitlc="NPFIT:HL7:Localisation" classCode="DOCCLIN" moodCode="EVN">
        <typeId extension="POCD_HD000040" root="2.16.840.1.113883.1.3"/>
        <custodian typeCode="CST">
        </custodian>
        <componentOf typeCode="COMP">
                        </componentOf>
        <component contextConductionInd="true" typeCode="COMP">
            <nonXMLBody classCode="DOCBODY" moodCode="EVN">
                <text mediaType="text/plain" representation="TXT">Refer to other payloads in this message for document content</text>
            </nonXMLBody>
        </component>
    </ClinicalDocument>
</payload>
<payload filename="eaf7a956-f09e-43a0-9a20-95696dc5acac.pdf" id="binaryDocument">J....YNCg==</payload>

. Any help would be appreciated!