code: public static Batch purchase(String id)
  			throws AuthenticationException, InvalidRequestException, APIConnectionException, APIException {
  		return request(RequestMethod.POST, instanceURL(Batch.class, id) + "/purchase", null, Batch.class, null);
  	}
docs: Purchase batch provided by id. This method corresponds to
  https://api.goshippo.com/batches/<i>BATCH OBJECT ID</i>/purchase endpoint
  defined in https://goshippo.com/docs/reference#batches-purchase
  
  @param id
  Batch object ID
  @return The Batch object after purchasing