I am using below AMPScript to retrieve access token for my subsequent REST calls but it is failing with "Bad Request"
%%[var @con,@body,@body1,@auth,@output,@response,@res,@callstatus ]%%
%%[SET @auth="Bearer xxxxxxxxxxxxxx"
SET @body="{"clientId":"xxxxx","clientSecret":"yyyyyyy"}"
HTTPPost("https://auth.exacttargetapis.com/v1/requestToken","application/json",@body,@callstatus) ]%%
%%=v(@callstatus)=%%