Unable to add nuget packages in my xamarin android project

In my case, I am using Acr.userDialogs package for opening an action sheet on button's click.
As soon as I click the button the error above appears, pointing to the code where action sheet is mentioned.

I tried adding Acr.UserDialogs to the android project but failed every time saying "Unable to add the package Acr.UserDialogs".

I have added the package in my main project.

Please help.