'redirect_uri' could not be validated

[screensforme]

I followed all the instructions in the readme.
Upon registering the smart app and successfully completing the verification of smartapp.
When I open my url 'https://5939-106-201-121-48.in.ngrok.io'
it shows
'redirect_uri' could not be validated

Am I missing anything ? Any help would be appreciated..

Also I could not find any REDIRECT_URI option in https://smartthings.developer.samsung.com/workspace/
I can see only Target URL which I have set properly