Error when attempting a PUT via webhook to update a ticket with an asset

I am trying to create a workflow that will automatically take the asset name from a custom field and submit a PUT request to update the ticket, associating the asset with the ticket without any extra intervention. I followed the API documentation to the best of my ability, but it doesn’t seem to mention the issue that I’m running into.

So I’m creating a PUT request using the web request tool to /api/v2/tickets/, with the body being:

The error I receive is:

The documentation doesn’t mention a “lf_asset_hostname” field, and when I add that to the body I get an invalid_field error. Does anyone know what I’m doing wrong here?