Integrating Google API: Assembly will not be loaded due to errors

I'd be grateful for any help on this issue. I don't think it is complicated, I just have a poor understanding of .NET.

I am trying to integrate a simple feedback system that submits data to a Google Sheet. I am have trouble specifically with adding Google's API dll file to Unity.

I used NuGet for Unity to download Google's Api. Because the API is compatible with .NET 4.5, I followed Microsoft's Using .NET 4.x in Unity guide. Here is what I've done so far.

1. Change Unity's Scripting Runtime Version to .NET 4.x Equivalent

2. Change Unity's Api Compatibility Level to .NET 4.x

3. Placed the Google.Apis.dll into Assets/Plugins.

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When I attempt to run the game I receive this error:

 Assembly 'Assets/Plugins/Google.Apis.dll' will not be loaded due to errors:
 Unable to resolve reference 'Google.Apis.Core'. Is the assembly missing or incompatible with the current platform?
 Unable to resolve reference 'Newtonsoft.Json'. Is the assembly missing or incompatible with the current platform?

Again, I would be grateful for any help. If you need more information let me know. I've also posted this question in the Unity forums.