At the end of the page, you will find four files:
csharp-marketpay-pos-api-20.1-documentation
Documentation on C# integration
ecrdrv-simulator-v21.1.0.0-dotnet-4.8-x86.zip
ECR simulator
marketpay-pos-simulator-gui-17.0.0.1_with_driver-5.6.26-7_dotnet_framework-4.6.2_x86
ECR simulator source code, to have code examples for ECR integration
ecrdrv-csharp-v20.1.0.zip
libraries to proceed with ECR integration
The ECR driver consists of 3 library files:
marketpay-driver-cpp.dll (.NET wrapper on core library, written in C++)
marketpay_pos_api.dll (C# driver interface, API definitions)
marketpay-pos-driver.dll (C# library which is C# to C++ converter)
The marketpay_pos_api.dll (API definitions) and marketpay-pos-driver.dll (C# wrapper on core) are .NET libraries so they both have to be included into project as DLL library reference in VisualStudio.
There is also 3rd necessary library marketpay-driver-cpp.dll which is Core library, written in C++. This file is not needed at build time because it's dynamically linked in runtime. But it has to be reached by .exe program.
The simplest way is to copy this file into directory where an .exe app is located. There are also two alternatives
PATH environmental variable
Put library into system directory like C:/Windows/System32.
The last two options are more difficult because of access permission or require the OS to restart.