Trouble creating my first Nova tool

I need to write my first tool for Nova but I'm stumbling at the first hurdle.

So far I've just used php artisan nova:tool xero-connector and run through the default helper choices. I've added the tool to my NovaServiceProvider and it appears fine in my sidebar. The link seems to route fine. The problem is rather than the default "We're in a black hole." Vue component the content area is just blank. There are no errors in my javascript console and none in my Laravel logs.

The tool.js file appears to have compiled ok in the dist directory.

I've uploaded what I have so far here: https://github.com/jolora/XeroConnector

I suspect the problem is in my package.json or webpack.mix.js as I had to update Mix due to npm failing to run (node-sass GYP err). That being said, I had a look at a couple of other tools I'm already using from third-parties and noticed one basically had an identical setup to me and it works fine on that tool.

Any advice on where I'm going wrong would be really appreciated.