I/O signals not showing in OPC UA client

I managed to establish connection between Robotstudio and UAexpert the OPC UA client I am currently using. The problem is that whenever I go in to the I/O signals folder in the OPC UA client, there are no signals or tags that is showing up. It's just empty

I've already tried to read and write to the virtual controller in I/O engineering. I also tried restarting the controller but that still does not fix the issue. What might be the problem?