Thank you for reaching out to the Zoom Developer Forum. I’m happy to help!
@alexmayo brings up a good point here - prior to being published, your app can only be installed by users, with developer privileges, on your account.
If you’re not logged in to Zoom and you attempt to install this app, you’ll be seen as a user that is outside of your account. Further, as your app is not published on the marketplace, Zoom isn’t able to find your client ID when looking it up on the marketplace. This is why you see the error invalid client_id.
You’ll want to make sure that you’re testing with a user on your account prior to publishing.
I hope that clears things up. Let me know if you have any questions.
Thanks,
Max