Unable to link Custom Plugin

I have created a custom plugin “BeaconMapPlugin” based on example plugin code models. It inherits from ProtobufPlugin and I instantiate it in setupPlugins() with:
new BeaconMapPlugin();
Everything compiles but seems to not link. I get the following error:
.pio\build\rak4631_5005\src\plugins\Plugins.cpp.o: In function setupPlugins()': D:\Data\PROJECTS\CowTrack\SW\MeshTrackGit\Meshtastic-device2/src\plugins/Plugins.cpp:67: undefined reference to vtable for BeaconMapPlugin’
This tells me that the compiled plugin code is not included in the link.
How do I make that happen?

Please put your code up on git somewhere. I’d gladly take a look.

What is this supposed to do?

OK. I forked meshtastic to evansf/Meshtastic which is public on github. To that I added BeaconMapPlugin and a BeaconMapMessage.proto. I added a CMakeListsUser file because the standard setup (very Linuxy) insists that my compiler is at /usr/… There are some changes to the platformio.ini and its variant in /WisCore_RAK4631_Board
This code is just adding a plugin that accepts a new protobuf and also accepts the Position protobuf. I am just setting up the playground for what I really want to do.
What is really going to happen here is a mesh where each node monitors a specific set of BLE beacons in its environment and is prepared to send a reply containing data on these beacons when a request is received. This mesh will be totally out of touch with any regular communications. Nodes can be attached to with an app via Bluetooth and the app can map the (approximate) locations of the beacons of the entire mesh.

I have resolved my issues here. The linker error info misled me. I now have a build with my own custom plugin that derives from ProtobufPlugin.
Thanks to mc-hamster for responding.