When creating enum list, got "Identifier expected" error

The problem is that 2ndOffers is not an identifier.

An identifier has to start with an underscore or a letter, it can contain digits, after that initial character.

So rewrite that identifier to be SecondOffers instead.

A technical version of the specification can be found here: Lexical structure - Identifiers which contains this part:

identifier_or_keyword
    : identifier_start_character identifier_part_character*
    ;

identifier_start_character
    : letter_character
    | '_'
    ;

identifier_part_character
    : letter_character
    | decimal_digit_character
    | connecting_character
    | combining_character
    | formatting_character
    ;

Basically, it has to start with "identifier_start_character" and can continue with zero or more "identifier_part_character", and "identifier_start_character" can only be a letter or an underscore.