Unity fails to load System.Net.Http script assembly

Hi, I'm working with Unity 2018.2.1f1 and I tried to use a certain function in Telegram.bot library and it gave me an error indicating that it requires an HttpClient instance as an argument.

So I imported a System.Net.Http package (v4.3.3) from NuGet and put it in the assets folder; The error went away but this other annoying error poped up that says :

Loading script assembly "Assets/Packages/System.Net.Http.dll" failed!

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And the thing is that unity lets me play the game anyways and the error pretty much doesn't matter, but when I want to get a build file, it comes back and bites me in the a**. So it's pretty annoying.

• "Scripting Runtime Version" and "Api Compatibility Level" is set to .Net 4.x

• "Scripting Backend" is mono.

• "TargetFrameworkVersion" is v4.7.1

• I'm pairing vscode with unity for the record.

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This is the script I'm trying to run:

 using UnityEngine;
 using Telegram.Bot;
 using Telegram.Bot.Types;
 using Telegram.Bot.Types.Enums;
 using System.Net.Http;
 
 public class TelegramSender : MonoBehaviour {
 
     void Start () {
         TelegramBotClient bot = new TelegramBotClient("<token>", new HttpClient());
         bot.SendTextMessageAsync(new ChatId(<id>), "Hello World!", ParseMode.Html);
     }
     
 }

And this code actually works and sends a "Hello World!" to my telegram channel but the error just stays there and doesn't let you to get an apk.

By the way I don't think there is a Web.config or app.config file in a unity project or at least I can't find it.

Here's an image of the error: