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[krishnilak]

Location : https://is.docs.wso2.com/en/latest/learn/writing-a-custom-oauth-2.0-grant-type/

e. Expand the OAuth/OpenID Connect Configuration and click Configure.
f. Enter a callback URL. For example, http://localhost:8080/playground2/oauth2client .
g. Click Add.

Add one more step to select mobile grant from the mangement console.

e. Expand the OAuth/OpenID Connect Configuration and click Configure.
f. Check "mobile" under "Allowed Grant Types"
g. Enter a callback URL. For example, http://localhost:8080/playground2/oauth2client .
h. Click Add.