How to dynamically format assertion in Postman

[michaelderekjones (Mike Jones)]

You need to read the other thread, which should explain why you can’t target elements like this.

Concade dynamic variable with pm.response.json() to fetch response value - Ask the Experts and Postman Tips - Postman Community

You cannot target the element using a string using plain old JavaScript.

You can however, use Lodash.