Having developed a lot of custom code, updating everything to the latest version would be too expensive. I have everything backed up and I have not deleted the previous posts, meta data etc. In fact (in the development site) replacing the plugin code with the old version everything works properly and I can see the messages before the change. So the easiest way for me is to “map” all the new messages (about 30) that use the tables fep_ * with the old system.
I imported a message (with manual operation in database), I see it in the wordpress backend, but it is not clear to me how to connect the metadata as the recipient etc.