Creating a conversation from a visitor returning an error "Lead Not Found"

Hello!

I am trying to create a conversation from a visitor per the doc: https://developers.intercom.com/intercom-api-reference/reference/create-a-conversation

I've tried setting `type` to `contact` as indicated. When passing a `user_id` like so:

{

"from": {

"type": "contact",

"user_id": "1234567"

},

"body": "Hey"

}

I received the error `Lead Not Found` and the conversation / contact with role lead are not created as expected.

How can I create conversations from visitors?

Additionally, in an ideal world I would be able to pass a singular user ID (not knowing if this is a visitor or existing Intercom user) and then create a conversation attached to the provided user if they exist, or instead a new user if they did not. Is this at all feasible?

Thanks for any help.