seenAt not working with ListNotificationsAsync

[mattbrailsford]

I'm trying to use ListNotificationsAsync to get the latest unseen notifications, but it doesn't look like passing seenAt works. I noticed there is a bug in the code and so have submitted PR #91, however after fixing this I seemed to get a "seenAt is unsuported" suggesting that the endpoint wasn't accepting it and I'm not sure why.

I checked the discord channel and I can see plenty of people suggesting it so I'm positive it should work, but I really don't know what it's not. Maybe you have some ideas.

I'm currently having to fetch the latest 5 results and then filter them based on their indexedAt date, but I'd much rather only fetch what's new.