code: func InvalidFormatError(ctx, target string, format Format, formatError error) error {
  	msg := fmt.Sprintf("%s must be formatted as a %s but got value %#v, %s", ctx, format, target, formatError.Error())
  	return ErrInvalidRequest(msg, "attribute", ctx, "value", target, "expected", format, "error", formatError.Error())
  }
docs: // InvalidFormatError is the error produced when the value of a parameter or payload field does not
  // match the format validation defined in the design.