APIConnect JSON array returned from external service

We have a Rest API that only contains "invoke" for the external Rest service in its assembly, without any mappings, so the API will only act as a gateway.

If the external service is called directly (for example, via SoapUI), it returns a JSON response that contains an array of objects. The array is nested 3 levels deep, starting at the root object.

Instead, when we call our API with the same request, we get a different response: instead of an array, we get an object corresponding to the last object in the array; there are no other array objects in the response.

Is there a way to fix this problem? Thank.