I am new as well but got it working after 2 issues.
Do you see anything in the /var/log/messages when u run the send command which could help identifying your problem ?
My sim card was not well inserted initially and got an error message.
You attempted to connect earlier, and that process is still running, so you can’t start a new one. The quickest way to solve that is to reboot. The more involved way is to use ps to find the thread and then kill it.