Short description of your issue:

I have an permanently error on amp-ad resize API on Open AdStream (OAS) adserver.

The error is:
476 "[CustomElement]" "Cannot resize element and overflow is not available"

Starting from this guide (https://github.com/ampproject/amphtml/blob/master/ads/README.md#ad-resizing) In my ad creative I wrote:

window.context.requestResize(300, 600);

Public URL to reproduce issue:

https://stadvtools.akamaized.net/xaxsis/common/googleAMP/AMP-AD/indexAmpDemo300600.html#development=1