The example is based on https://github.com/OrdnanceSurvey/OS-Data-Hub-API-Demos/tree/master/OSVectorTileAPI/OpenLayers and with the API key having access only to open ...
Alternatively, you can use the tileserver-gl-light package instead, which is pure javascript (does not have any native dependencies) and can run anywhere, but does not contain rasterization on the ...