docs: def validate_number(self, number):
          """ Checks if a number looks somewhat like a E.164 number. Not an
          exhaustive check, as the API takes care of that
          """
          if not isinstance(number, str):
              raise ElksException('Recipient phone number may not be empty')
          if number[0] == '+' and len(number) > 2 and len(number) < 16:
              return True
          else:
              raise ElksException("Phone number must be of format +CCCXXX...")