Mock Servers Dynamic Response value within Array - path.to.variable

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1

I have a mock server that successfully follows this request body and response body pattern:

REQUEST:

{
  "products": [
    {
      "inventoryAction": "string",
      "inventoryType": "string",
      "productId": "55",
      "storeId": "int"
    }
  ]
}

RESPONSE:

{
  "errorMessage": "string",
  "inventory": [
    {
      "inventoryType": "Available",
      "productId": {{ $body 'products.productId' 'DEFAULT' }}
      "quantity": 0,
      "storeId": "int"
    }
  ]
}```


Now my only question is, how do I get `productId` to reply 55? It keeps erroring out and replying `DEFAULT` I am familiar with dynamic response as per the documentation here: 
https://learning.postman.com/docs/designing-and-developing-your-api/mocking-data/creating-dynamic-responses/#using-template-helpers 

How do I write the `path.to.variable` part for a value within an array? 
If the array was not there, I know how to structure the path, but the array is throwing me off.

I have looked through here as well, still no luck:
https://www.npmjs.com/package/object-path

Many thanks in advance!

J