I was playing with the API to see how things work and when I tried to send something to the feed it didn’t show up after receiving the notification. That’s when I noticed that it was defaulting to my old prepaid account number instead of the new current account number.
I can’t test this, as I only joined as a Current Account user (so it obviously send feed items to the right account).
This might be something you should raise on the Monzo Developers’ Slack Channel.
This confused me at first also. I just ended up using Insomnia (a REST client) to make my calls and using the playground for reference. Another popular REST client is Postman.