I don’t really know anything about Asterisk. I’m here to learn. However I’ve been a programmer for 22 years. So I think I might have a valid guess: I think you need another closing parenthesis at the end of line 1. I see 4 opening parenthesis and only 3 closing parenthesis.
In Emacs, when you position the cursor over a bracketing symbol (opener or closer), it highlights both brackets of the pair in green. If it cannot find a match for that bracket, it highlights it in purple.
This works in any text file; it doesn’t need any special language-specific rules for this.