Adding Message to Ticket object in Online REST API

Having existing Ticket with given ID, how I can create full (with body) TicketMessage and add it to mentioned Ticket.
I could not see field TicketId in any  endpoint of /TicketMessage
https://docs.superoffice.com/en/api/reference/restful/rest/TicketMessage/index.html
Am I missing something?

I see field “Ticket”, but I assume it can’t work this way that I’m put whole Ticket object just to referenced.

(esp. that in example I see it is null)

Please help me with that one.