How do DMs on nostr work??

I replied to a DM using Amethyst.
My reply doesn't show up in any other nostr client, ever. Refresh. Restart. Nothing. It looks like I ghosted them.

My reply sometimes shows up in Amethyst. Sometimes it doesn't. I can't figure out what makes the reply visible sometimes.

I have no confidence the recipient has seen my reply. Or that it was even sent out to the network for that matter. If I saw my reply in at least one other client that would give me some confidence it was sent.

What would you suggest?