Token Comma expected. / Token Literal expected. / Token RightParen expected.

An M syntax error — the parser expected a token that isn't there.

Why it happens

• A missing comma between record fields or function arguments.
• Unbalanced parentheses, braces or brackets.
• A missing in, or a stray or unclosed quote.

How to fix it

1. Open the Advanced Editor and balance every (), {} and [].
2. In a let block, every binding except the last needs a trailing comma.
3. Confirm each string literal is closed with a matching quote.