Unable to access JSON child property [closed]

I am making a REST API call with POST method to a third party system. I am passing JSON on the request body of the call.
Below is a mockup of the JSON which I am passing on the request:

{
    "table":"xxx",
    "fields": {
        "service":"xxxxxxxxxxx",
        "opened_for":"xxxxxxxxxx",
        "short_description":"xxxxxxx",
        "description":"Test"
    },
    "includeErrors":"true"
    
}

The third party system before processing the message first looks if the request has the property “service” under the fields property using hasOwnProperty. The condition used is below:
(if (fields.hasOwnProperty('service')).
For the above JSON request body, this condition is getting met and further processing happens. During further processing, third party system is trying to fetch the value of the service property fields['service'].value, for the above JSON request this code is unable to fetch the service property value.

I tried the below json request body:

{
    "table":"xxx",
    "fields": [{
        "service":"xxxxxxxxxxx",
        "opened_for":"xxxxxxxxxx",
        "short_description":"xxxxxxx",
        "description":"Test"
    }],
    "includeErrors":"true"
    
}

For the above request body, fields['service'].value is able to fetch the service property value but it fails the condition (if (fields.hasOwnProperty('service')).

I need inputs on how the JSON request body should be so that fields['service'].value fetches the service property value and also the condition (if (fields.hasOwnProperty('service')) is satisfied.

I tried to convert the JSON request body as an object, but that did not help resolve the issue.