your signature seems ok - tested here
is your meeting sdk app created before 11. Feb 2023 ?
if yes, you have to use the SDK Credentials (SDK Key, Secret), not the OAuth credentials (Client ID, Secret)
if this is not the problem, you should start with the example on github (CDN version)
the CDN version is ready to use with a few simple steps
CDN/js/index.js:20 var CLIENT_ID = "YOUR_CLIENT_ID_OR_SDK_KEY";;
CDN/js/index.js:26 var CLIENT_SECRET = "YOUR_CLIENT_SECRET_OR_SDK_SECRET;
CDN/js/index.js:112 ... "/meeting.html?" // replace '/' with './'
CDN/js/meeting.js:31 leaveUrl: "/index.html", // replace '/' with './'