Twigpack outputs empty strings on Docker

[ignism]

I have a manifest file sitting at http://localhost:8080/build/manifest.json and I configured my twigpack.php as follows:

// Manifest file names
'manifest' => [
    'legacy' => 'manifest-legacy.json',
    'modern' => 'manifest.json',
],
// Public server config
'server' => [
    'manifestPath' => '/build/',
    'publicPath' => '/',
],
// webpack-dev-server config
'devServer' => [
    'manifestPath' => 'http://localhost:8080/build/',
    'publicPath' => 'http://localhost:8080',
],

However, twigpack can't find my modules it seems. and doesn't output anything. Is there a way for me to debug this, whether Twigpack found the manifest at all?

EDIT:
I went through my logs and indeed, Twigpack can't find the file.
[warning][nystudio107\twigpack\helpers\Manifest::reportError] Manifest file not found at: http://localhost:8080/build/

Any idea what I'm doing wrong?

[ignism]

setting publicPath to 'publicPath' => 'build/', did the trick