Building an application also needs the DLL stub library in $(OPCUA)/lib/$(T_A), not just the DLL in $(OPCUA)/bin/$(T_A).
(Careful: the stub is named differently between MSVC and MinGW.)
The application, on the other hand, should only install a copy of the DLL for distribution. The stub is not needed for running an application, just for building it.
Building an application also needs the DLL stub library in
$(OPCUA)/lib/$(T_A), not just the DLL in$(OPCUA)/bin/$(T_A). (Careful: the stub is named differently between MSVC and MinGW.)The application, on the other hand, should only install a copy of the DLL for distribution. The stub is not needed for running an application, just for building it.