An add-in can add one or more ribbon commands to the Extensions->API command gropup. Therefore the class Eplan.EplApi.Gui.RibbonBar provides a function AddCommand which should be called in the OnRegister() method of the add-in class:
The function AddCommand(text, command line) adds a button (i.e ribbon command) with the text "CSharpAction" and assigns the action "CSharpAction" to it. The button is then visible in Extensions->API command group. It is also possible to add it to a custom command group that exists in either persistent or a custom tab.
Ribbon commands are always assigned to an action. This can be either custom action (created by API) or already existing existing action.