I've noticed that my replies are being affected. Like I can read a note, but I get that popup when I submit a reply. I never see the reply if I don't pay the relay fee. The popup is suggesting that I pay to write to that relay. Without the popup, wouldn't I see nothing and never know that my note wasn't written? If they don't have outbox, then I'm not sure how they could see my notes if we don't have overlapping relays.
Discussion
But I also have a very low understanding of this relay model.
The note will go to your own outbox as well, so you should always see the reply (I will check later to make sure this is happening).
But if they have an inbox that is paid and you don't pay, they might not see your reply for sure. But that's kinda what they want if they added a pair relay to their inbox list.