I am not a prom.ua developer, and unfortunately I cannot answer with accuracy which API method can correspond to one or another functionality of their control panel interface.
I know that at the moment we have an action that allows you to import messages from prom.ua into processes + an action at the stage that allows you to send a response based on the last comment in the process.
According to the public documentation
https://public-api.docs.prom.ua/ - I do not observe any other methods regarding messages.