It's a pity that this sort of feature is done with a custom ad-hoc HTTP protocol instead of using a message queuing protocol like AMQP or STOMP. Those are designed for this kind of thing and already have libraries available, they avoid the need for busywork polling and avoid the need to break work up into batches client side. You should just be able to submit messages containing work to a queue and then let the broker inform you when new responses arrive on the response queue if you're connected. If you're not connected they buffer up for a while until you reconnect and drain the queue.

The advantage of that approach would be that latency could be minimized or tiered. Instead of a single "one batch with maybe up to 24hr latency" the offer could be a series of tiered queues with different SLAs and costs, and you can pick which you submit your work to depending on how important it is.

I wonder why they went for this custom JSON/HTTP approach instead. Maybe they feel that they can't expect developers to understand anything other than POSTing JSON.