When using the JavaScript SDK to enable client side OAuth flow, I'm running into this issue: Uncaught TypeError: Cannot read properties of null (reading 'postMessage')

And the page gets stuck with the message Authorizing Application.

Steps to reproduce —

1. Go to: https://api.stackexchange.com/docs/js-lib
2. Scroll all the way down and click on the Run Example With Version 2.3 button
3. Click on Approve to authorize your account

This is impacting my app as described here — Customizable, short URLs for Stack Overflow profiles