Question Does IL2CPP require special configuration for handling private classes in managed DLL

I made a managed DLL and used it in my project.
Error when building with il2CPP backend,some like this:

C:/workspace/Work/U3D/SpaceVS_GP/Library/il2cpp_android_armeabi-v7a/il2cpp_cache/76825AC61B1BA8D66DD99560ACB7A813.o: C:\workspace\Work\U3D\SpaceVS_GP\Temp\StagingArea\Il2Cpp\il2cppOutput\CibaLibs_CodeGen.c:s_methodPointers: error: undefined reference to 'URCertificateHandler_ValidateCertificate_m4F2F79D3C38442DE00C68371D6952A9E0682BC07'

URCertificateHandler is a private class in the DLL project.

I created the DLL following the unity doc:
https://docs.unity3d.com/Manual/UsingDLL.html

Does IL2CPP require special configuration for handling private classes?
Or only handle public classes?