I'm writing this comment down in case others are looking into the same
issue as I have. I tried to do a workaround by setting it up as 2
subscriptions, one with the oldState and another with a newState but
going to separate urls. And theoretically, it works if your user is just
ticking and unticking that one checkbox. However, if there are more than
1 checkbox that gets ticked/unticked, then it doesn't trigger the
newState and oldState. The event subscription api operator only has eq,
ne, gt and...