Connect to Oracle database in dotnet mvc application

As @Lesiak stated, I used the wrong package (the right one is Oracle.ManagedDataAccess.Core.dll). But that is an error someone else might fall in too. Because when you download the zip file from Oracle Link the dll name is Oracle.ManagedDataAccess.dll instead of Oracle.ManagedDataAccess.Core.dll that's error prone.

For me, the solution was to install the Oracle.ManagedDataAccess.Core NuGet package only. I had Oracle.ManagedDataAccess installed as well and I needed to uninstall them to fix the error.