Thanks for the hint, I'll check it out 👍

This is great to see as I have HA running on an old iPad in the kitchen and it works fine but since Power Card Plus has been the primary card on the main dashboard, it's not worked on the iPad so hopefully this means that the old tech has a future again!

Can you check if this fixes the issue, there are still two ?? in there, but maybe it's fixed now
power-flow-card-plus.js.zip

Edit: please make sure in the console shows the version 0.2.0-414 to make sure you are using the correct version

I've had a look deeper in the code at this (I'm pretty new to HA and am using an old iPad in the kitchen too!).

The issue comes from superstruct where this.failures is a function with a nullish operator inside. This is because the node modules aren't being transpiled with iOS 12 as a target, just to the current version of node.

So:
babel.config.js gets ["@babel/preset-env", { targets: { node: "current", ios: "12" } }]
and the rollup.config.js gets:

babel({
        exclude: /node_modules\/(?!superstruct)\/.*/,
        babelHelpers: "bundled",
      }),

I'll send over a PR