WSDiscovery 'Hello' message isn't recognised by dasHost.exe

Question

I'm trying to use WSDiscovery in .Net8. This isn't supported directly but I have got a client application working that is able to send probe requests and receives probematch replies from dasHost.exe

However I can't manage to get my server application to work. It sends the 'hello' packets but it seems that it's not accepted by dasHost because when my client app sends a probe request it doesn't receive any probematch replies.

Has anyone managed to make WSDiscovery work in .Net 8 (or 6) or know of a library/nuget that implements it?

A sample of the 'hello' packet my client sends is included here (this is multicast to port 239.255.255.250:3702):

<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope" xmlns:a="http://www.w3.org/2005/08/addressing">
	<s:Header>
		<a:Action s:mustUnderstand="1">http://docs.oasis-open.org/ws-dd/ns/discovery/2009/01/Hello</a:Action>
		<h:AppSequence InstanceId="63838239676" MessageNumber="1" xmlns:h="http://docs.oasis-open.org/ws-dd/ns/discovery/2009/01"/>
		<a:MessageID>urn:uuid:e59ab8f8-1d5e-44ac-ad17-9b7bc75d95a5</a:MessageID>
		<a:To s:mustUnderstand="1">urn:docs-oasis-open-org:ws-dd:ns:discovery:2009:01</a:To>
	</s:Header>
	<s:Body>
		<Hello xmlns="http://docs.oasis-open.org/ws-dd/ns/discovery/2009/01">
			<a:EndpointReference>
				<a:Address>http://dtd-lt35:7042/LicenceServer/LicenceServerService</a:Address>
			</a:EndpointReference>
			<d:Types xmlns:d="http://docs.oasis-open.org/ws-dd/ns/discovery/2009/01" xmlns:dp0="http://LicenceServer">dp0:ILicenceServerService</d:Types>
			<XAddrs>http://dtd-lt35:7042/LicenceServer/LicenceServerService</XAddrs>
			<MetadataVersion>0</MetadataVersion>
		</Hello>
	</s:Body>
</s:Envelope>

The WSDiscovery spec states that 'A Hello MUST be sent multicast to "urn:docs-oasis-open-org:ws-534 dd:ns:discovery:2009:01"' but then it also states that for probe requests and yet those are working.