Check your connection name and, if you're forwarding messages, your endpoint URL.
One of the connection-setup wizard's step 2 fields didn't pass validation. The connection name is required, and if you chose "Also send messages to my own server", the endpoint URL must be a full https:// address.
Fix the connection name if needed.
If you're forwarding, check that your endpoint URL starts with https://.
Or choose "Use Avox for everything", which needs no URL.
Click Next again.
Still stuck? Send AVX-3006 to hello@theavoxai.com along with what you were doing when it happened.