After inserting all the correct information , if you are unable to Generate new access token and receiving following error OAUTH_APP_ACCESS_DENIED.
You have to enable users to Self-authorize
Setup >> Manage Connected Apps[Lightning]/ Connected Apps under Manage Apps[ Classic] >> Edit against connected app >> Select All Users may self-authorize in permitted users picklist
You are all set. Go ahead and try again and you will be prompted with allow window
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