Hi Joan,
Thank you for your post. Square brackets mean array in json. So, I recommend that you use the Script assertion and parse the received response using Groovy.
You can start with the following script which gets the response content:
import groovy.json.JsonSlurper
def response = messageExchange.response.responseContent
def slurper = new JsonSlurper()
def json = slurper.parseText response //received json
def result = false // result of the assertion
...
In your particular case, I've managed to get the valid assertion with the following settings for the JSONPath Match Assertion:
JSONPath Expression
$.features.*
Expected Result:
[AAAAA 16478396302]
Examples can be found in this article:
JSONPath Match Assertion: https://support.smartbear.com/readyapi/docs/testing/assertions/reference/property/json-match.html