Hi @zezulatomas , my initial assumption is that it has to with the privacy and user data management framework for published apps. Since the original creator of the meeting (User B) in the first example did not provide consent for the app to access their data, the webhook will not trigger.
Co-host =/= host and they do not assume full permissions available to original host so I am not surprised the app does not receive meeting event info if user b did not approve the app for their meetings.
I am moving this post to App Marketplace . @kwaku.nyante , can you offer some insight to confirm or clarify my response from the security perspective?