The DDE (Dynamic Data Exchange) is a windows service, which helps to populate the data from one application into another.
The Trading Station or Lua themselves do not support DDE, so you need an extension module for Lua which provides DDE services.
You must download and install it before using the DDE offers publishing strategy.
An extension module and description are available here.
https://fxcodebase.com/code/viewtopic.php?f=31&t=4159