highcharts-export-server always produces blank PNG - highcharts

Question

I'm trying to use highcharts-export-server in command-line/batch mode. I've installed the latest version (2.0.28). I'm running Windows 10 with Node 12.
I'm running it from the command line using the following command:
highcharts-export-server --nologo 1 --logLevel 4 --options chart.json --outfile chart.png --type png --width 500
The console output says:
starting highcharts export server v2.0.28...
Fri Sep 25 2020 15:07:48 GMT+0100 (British Summer Time) [verbose] attaching exit listeners to the process..
Fri Sep 25 2020 15:07:48 GMT+0100 (British Summer Time) [verbose] Pool started:
maxWorkers: 1
initialWorkers: 1
workLimit: 60
listening to process exit: true
Fri Sep 25 2020 15:07:48 GMT+0100 (British Summer Time) [verbose] phantom 1 - spawning worker
Fri Sep 25 2020 15:07:48 GMT+0100 (British Summer Time) [verbose] starting export
Fri Sep 25 2020 15:07:48 GMT+0100 (British Summer Time) [verbose] attempting to export from raw input
Fri Sep 25 2020 15:07:48 GMT+0100 (British Summer Time) [verbose] phantom - received work, finding available worker
Fri Sep 25 2020 15:07:48 GMT+0100 (British Summer Time) [verbose] phantom - found available worker
Fri Sep 25 2020 15:07:48 GMT+0100 (British Summer Time) [verbose] phantom 1 - starting work
Fri Sep 25 2020 15:07:52 GMT+0100 (British Summer Time) [notice] phantom worker 1 finished work ??? in 3562 ms
Fri Sep 25 2020 15:07:52 GMT+0100 (British Summer Time) [notice] phantom worker 1 - process was closed
Fri Sep 25 2020 15:07:52 GMT+0100 (British Summer Time) [notice] terminating, killing all running phantom processes
...but although a chart.png file is created and has the correct width, it's blank (transparent):
This is the content of the chart.json file, which I took from one of the examples on the Highcharts website:
{
chart: {
type: 'bar'
},
title: {
text: 'Fruit Consumption'
},
xAxis: {
categories: ['Apples', 'Bananas', 'Oranges']
},
yAxis: {
title: {
text: 'Fruit eaten'
}
},
series: [{
name: 'Jane',
data: [1, 0, 4]
}, {
name: 'John',
data: [5, 7, 3]
}]
}
Note: I'll mention that when I first tried to install highcharts-export-server I hit a different problem which was that I couldn't run it at all (it failed with uncaughtException: TypeError: "file" argument must be a non-empty string). After some googling I found some blog posts suggesting that I needed to install PhantomJS first, and to use the --unsafe-perm option. So, the commands I actually used to install it was:
npm install phantomjs --unsafe-perm
npm install highcharts-export-server --unsafe-perm
Oh, and it wasn't until some time later that I realised I might have to install Highcharts itself :-) So I did that too (npm install highcharts), but it didn't actually seem to make a difference.

Answer 1

In case this helps anyone else, here is the full conversation about this issue on the Highcharts Forum.
In summary, it turned out that the NPM package was improperly installed (due to a firewall issue).
This wasn't apparent from the installation logs, but the effect was that in the node_modules/highcharts/export-server/phantom/export.html file there was a script block that should have contained minified JavaScript but that actually contained only lines saying undefined;.
The fix in my case (to work around the firewall issue) was to specify an http URL for the CDN when installing Highcharts Export Server, rather than the default URL which uses https. Once I'd done that, the export.html did contain the minified JS code, and the tool worked correctly.