I have recently been working on an Umbraco 7 based site.
Umbraco is a little strange to get used to for a developer due to the fact that it overrides some the MVC defaults, and has different types of controllers such as Surface controllers (which are used to render content) and Custom Controllers (that can be used to intercept Umbraco content pages) – more information can be found at http://stackoverflow.com/questions/25603722/surface-controller-or-custom-controller-in-umbraco-7 for anybody interested in this.
I thought it might be a good idea to investigate Merchello as the site in question only had a small number of products (the Merchello product catalogue typical of many Umbraco packages stores its data in the Umbraco content tree, which is good for web pages but not so good if you have 30,000 products).
Anyway I only had a few products, so I quickly set this up and then thought about adding the Merchello Paypal plugin.
Merchello is available at: http://merchello.com/ and the Paypal payment provider is available at https://our.umbraco.org/projects/collaboration/merchello-paypal-express-payment-provider/
Again fairly easy to setup, but it doesn’t work. An error message appears when you try to access your Paypal account for real. This is because a DLL is missing from the package.
The answer is to download the Merchello example site from https://github.com/Merchello/Merchello, then open the Paypal plugins in Visual Studio, ensure any nuGet packages are restored, and then build. Copy this DLL into your website project, and hey presto! Everything works!
If anybody would like a more detailed explanation please comment and I’ll fill this post out a bit.