Web API in GrandNode can be extended with an additional plugin. I will describe shortly how we can implement it in the newest version of GrandNode.
Download the source code of plugin
Please download the plugins source code here.
Extract the zip file and please copy the whole content to your GrandNode directory. You should copy it to Source code -> Plugins folder.
Now, we need to add existing project to our solution. In GrandNode solution, please go to Plugins section, right click on it and select Add -> Existing project.
If you want to get the compiled version, which you will be able to install in your GrandNode. Right click on the project and select the "Build" button. It will rebuild the whole project and create a compiled version of plugin. Files will be available in the Grand.Web -> Plugins folder.
Now you can run your GrandNode, login to your admin panel and go the Plugins list. Probably you should see the Extended API plugin. Install it.
This plugin allows you to use data stored in the Orders, Payment transactions, Shipment and Merchandise returns collections in GrandNode database.