DllNotFoundException when using .so file

[rangolee302]

I try to test if I could use .so file on the project and found this Unity - Manual: Native plug-ins for Android on the docs. At the bottom of the page there is a zip file which is a simple project that demonstrate how to use .so in Unity project. So I build a apk and run it on my phone and the error prompt
DllNotFoundException prompt out .Where did I go wrong?

Here are some screenshots of the builds settings

And here are the errors:

[rangolee302]

Problem Fixed. I use ndk-build to compile the source code again and copy the generated .so file to replace the .so in the Plug-ins/Andriod/ folder and it works. I don’t know if it is the matter of the my phone model (I am using Galaxy S8 Plus) or it is the config problem in the .mk files