Web Messaging SDK: Passing CRM ID to startChat()

Trying to push a CRM customer ID into the Web Messaging SDK via the startChat() call. The goal is to have that ID available in the routing data or agent view. Here is the snippet I’m using:

const guest = {
 name: 'Test User',
 email: 'test@example.com'
};

const chatOptions = {
 guest: guest,
 routingData: {
 crmId: 'CRM-12345'
 }
};

genesys.cloud.startChat(chatOptions);

The chat connects fine. The agent sees the name and email. The CRM ID is nowhere to be found in the transcript or the contact attributes. Am I missing a step to map routingData to a custom attribute before the chat starts?