Deveo plugins are what identify external applications making requests to the Deveo APIs. You can use any plugin you wish, as long as it has been granted with the appropriate permissions, of which the needed one in this case is the ability to create events. The available plugins are listed in the Apps app in Deveo and for each plugin you'll find a plugin key in their details. If you are unsure of which plugin to choose, it's safe to go with the API Access plugin.