As far as I understand, the game considers you "active" or "idle" depending on what you've been doing in the past few minutes. I think after five minutes of no AP spent, the server stops bothering to send you non-Union help requests, so don't keep refreshing the raid page over and over for that long. Running a Gem Gacha seems to bring you back into the land of active without spending AP.
I haven't properly tested it, that's just the impression I have.