Greetings!
I inherited this thread, and I wanted to follow up on what's going on here. This kind of HTML5 bundle from now on can only be uploaded through the UI and not the API. So, the error you're getting is expected. There are some features that are in the UI and not the API; this happens to be one of them. When I asked if we could add it in the feature, the response was that we had decided not to add that in the API in the future.
We are currently working on creating a better error to make it clear that there are some things you can only do in the UI.
Best,
Nadine Wang, Google Ads API Team

ref:_00D1U1174p._5001UZV1tL:ref