Hey @ZoomLinkManager,
Thank you for reaching out to the Zoom Developer Forum. I would first make sure that you are making the function call to ZoomMtg.join() as outlined here. Then, ensure that the signature you generate is correct and matches the documentation.
On that same note, where are you getting the client_id and how are you using it in your code? I would make sure that you are getting the SDK Key and Secret from the App Credentials tab of your SDK Credentials app.
I hope that helps! Let me know if you have any questions.
Thanks,
Max