Web Messaging participant attributes missing in Inbound Message flow

Architect & Flows
1

Here’s the payload from the Web Chat session:
{
“attributes”: {
“customerTier”: “Gold”,
“source”: “web”
}
}

I’m trying to access these inside an Architect Inbound Message flow using sys.attributes.customerTier, but it comes back null. The standard sys object doesn’t seem to expose the participant attributes for Web Messaging like it does for Voice. Is there a specific path or a Get Data action required to pull these?