Yes, I changed it to the master node:

I put this on master and other node.
I think the error message is not clear. When I put a dummy IP it runs and just waits. But with the correct IP (node with rank 0) it returns that error.
For that command, it returns the worker IP and name.
I just changed the batch_update_size to 1, and ran the code with rank 0 and other with rank 1. I also changed the master address and port.
I also had to specify the backend to avoid other error as this:

Any clue to check? Thanks