Hi @jeremy5,
Welcome to the Auth0 Community!
I understand you have experienced issues with the invalid client id error when using the Auth0 PHP SDK.
After my tests, I could not reproduce the same issue. Instead, I was able to successfully launch the app without any errors when using the Auth0 PHP Quickstart.
In this case, could you try using the Auth0 PHP Quickstart guide and see if that resolves your issue?
I am looking forward to your response.
Thanks,
Rueben