Good, if you use VW SDK 2019, that is another story, then you must use toolset V141.   The bad news is that under Windows you cannot use Debug version of your plugin in a released VW version... which is compiled as Release. That is has to do with a design choice of Microsoft where the C Runtime of Debug and Release cannot be used together. As, since VW 2018, TXString ist implemented internally as a std::string, you cannot call a TXString from your plug-in through a call using a TXStrin