Hi @Glenn1, welcome to the forum!
An HTTPS Error 401 indicates to me that your auth header is incorrect. Looking at this line:
In my application, the grant_type I’m using is account_credentials not client_credentials, so give that a shot.
EDIT: Just to add, I’m also specifying my account ID in the request, which I don’t see in yours:
oauth/token?grant_type=account_credentials&account_id=${MY_ZOOM_ACCOUNT_ID}