One of my debugging tools when something doesn't seem to work as expected on iOS is to tell NativeScript to output the metadata while it is building the application. The easiest way to do it is:
TNS_DEBUG_METADATA_PATH="$(pwd)/metadata" tns build ios
This will create a metadata-xxxx folder (where xxx is the platform) in the root of your project. This folder will contain an XML file for EACH item it generated meta data for inside your project. Please note this DOES slow down the build time as it has to create each file. But it is worth it for the diagnostics it provides.
Then I just look at the meta data and I can see if it first created a file for the plugin I'm working on, and if so, what is the exact exposed methods.
The second tip is for those people using TypeScript; if you would like the .d.ts file for your plugin you can do:
TNS_TYPESCRIPT_DECLARATIONS_PATH="$(pwd)/tsc" tns build ios
And it will create a tsc folder with the .d.ts files for each of the items it built metadata for.