@Irfan-Khan-0, I just tested it an it's working for me.

Could you try clicking the "Regenerate" button to regenerate the Client ID and Client Secret under App credentials, then copy/paste those into your user profile?

And make sure the "SmartThings Device Cloud Credentials Client ID" values (starts with st-) and the "SmartThings Device Cloud Credentials Client Secret" value match those values under App Details?

If those 4 values match, and you have these URL's setup, it should work:
Authorization URI: https://www.triggercmd.com/oauth/authorize
Token URI: https://www.triggercmd.com/oauth/token