How can I add a SWIG-generated C++ DLL reference to a C# project?

I am using SWIG to generate a DLL that will expose C++ functionality to a C# project. At the moment I:

1. Define a SWIG interface file

   %module example
   %{
   /* Includes the header in the wrapper code */
   #include "../pointmatcher/PointMatcher.h"
   %}
   
   ...
   
   %include "../pointmatcher/PointMatcher.h"
   
   

2. Use SWIG to generate a .cxx wrapper

   swig.exe -c++ -csharp -outdir csharp example.i
   
   

3. Compile the .cxx wrapper with MSBUILD via CMake

   # create wrapper DLL
   add_library(example SHARED ${WRAP_CSHARP_FILE})
   target_link_libraries(example pointmatcher)
   install(TARGETS example
           ARCHIVE DESTINATION ${INSTALL_LIB_DIR}
           LIBRARY DESTINATION ${INSTALL_LIB_DIR}
           RUNTIME DESTINATION ${INSTALL_BIN_DIR})
   
   

I then have a DLL file (example.dll) which I can inspect via Dependency Walker, and confirm that methods are being exposed as follows:

However, when I try to add this MSVC DLL as a reference to a C# project I get the error "It is not a valid assembly or COM component".

Based on answers at How can I add a VC++ DLL as a reference in my C# Visual Studio project? I have confirmed that SWIG itself generates P/Invoke calls, and that tlbimp doesn't recognise the DLL either.