C++ Transition Guide for 4.22

hi
ive been trying to update this plugin
https://forums.unrealengine.com/community/community-content-tools-and-tutorials/60077-the-re-inventing-the-wheel-thread

i have this error, TestCar is the name of the plugin.


Severity Code Description Project File Line Suppression State 
 Error    LNK2001    unresolved external symbol IMPLEMENT_MODULE_TestCar    CarPluginProject    J:\UE4Projects\CarPluginProject 4.22\Intermediate\ProjectFiles\LINK    1

what has changed since 4.20 that would cause an error like this? thanks