The error says it all. REST API calls are no longer supported by the API in Graph API v2.1. You should get up to date and use the official Facebook SDK to create your Facebook application.
v2.0 is still available until August 7, 2016. So, you can still use the REST API if you like. You are probably getting this because your API calls are either unversioned or they are versioned to v2.1. See this