If your client doesn't show it, use something like rust-nostr (in bindings of your choice, e.g. python or Js) and check the logs what relays reply to you when trying to send something. They either return success or give you a response like you're blocked or you are not paying or you are not using a NIP05 or whatever they want.  

 I have to see these all the time when people put in paid/closed/private relays in their public inbox relays and a DVM tries to reply and gets all kinds of reasons why it's not allowed to write on PUBLIC inbox relays 😅