How to update a custom field on a request item?


I’m looking for a way to update a ticket’ request item field.

I checked on the API documentation, but custom fields are not included on the “Update a Ticket” API endpoint.

Also, I checked through the SDK, but I can’t find it either.

In both cases I can see how to update fields related to the ticket directly, (like priority, status or source, even custom fields), but I can’t seem to find a way to update fields on the request item, added through the service catalogue.

Is there a particular endpoint or method that allow me to perform this task?