Error 400

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Hide Details Error Summary 400 Bad Request The redirect URI you provided has not been whitelisted for your application. Please add your redirect URI in the 'Allowed Return URLs' section under 'Web Settings' for your Security Profile on Amazon Developer Portal. Request Details scope_data=%7B%22alexa%3Aall%22%3A+%7B%22productInstanceAttributes%22%3A+%7B%22deviceSerialNumber%22%3A+%221%22%7D%2C+%22productID%22%3A+%22HerokuforApp%22%7D%7D scope=alexa%3Aall response_type=code client_id=amzn1.application-oa2-client.xxxxxxxxxxxx redirect_uri=http%3A%2F%2Fwebappalexa.herokuapp.com%2Fcode

Why is this happening even though I have added the endpoint uri? (https://webappalexa.herokuapp.com)