I am getting a RestClient::BadRequest: 400 Bad Request when hitting the endpoint "/restapi/oauth/token"

Here is my code.

 def get_new_tokens                   url = "#{BASE_URL}/restapi/oauth/token"

  hash = {

   grant_type: "password",

   username: username,

   password: password,

   extension: extension

  }

  response = JSON.parse(RestClient.post(url, hash, self.class.headers))

  puts response

  self.update(

   access_token: response['access_token'],

   refresh_token: response['refresh_token'],

   expires_at: DateTime.now + response['expires_in'].seconds,

   refresh_token_expires_at: DateTime.now + response['refresh_token_expires_in'].seconds,   

  )

 end  

I cant figure out what the issue is. I am not getting any description back on the 400 error. Any help would be much appreciated.