Create a new ticket. Not every channel that accepts replies can have a ticket opened on it: opening one has to create a real conversation on the marketplace, which is verified for Kaufland, Fnac, Veepee and Mirakl but not for Cdiscount, TikTok Shop, Reverb or Backmarket. Creating a ticket on one of those returns error code 4013 - reply to the imported ticket with POST /messages instead.

On Mirakl the first message opens a thread against the order the ticket carries, addressed to the recipients named by the channel's "Default messages recipients" setting. A Mirakl channel with that setting still at "Not selected" could never deliver a reply, so creating a ticket on it returns error code 4024 - see POST /messages for where to set it.