Sorry. Let me reframe my question.

I know the message_id and the passing parameters value for raiserror().

e.g..

raiserror(60071, 10, -1, @a, @b-2)

Error text for 60071 is "Product %S is not available in %S"

so raisederror would be "Product @a is not available in @b-2". I need to capture this text.