How do you coordinate/discuss between moderators?

Over at r/ankylosingspondylitis (a sub for an autoimmune disease) we've tried to use the reddit chat feature to create a group chat for the moderators. But the notifications for group chats doesn't seem to work reliable at all, so we need something else. People miss out on chat messages and only see them months down the line, if at all.

How do you all coordinate and communicate between moderators in a subreddit? I'd like to avoid using external chat clients like whatsapp/element/signal/whatever. I.e. preferably keep reddit's concerns inside reddit.