Hi JC. Welcome to the forums.
You don’t need to use expression tags to read and write to PAC Control tags. Use the Ignition Opto 22 module.
First start by enabling the Opto 22 driver.
From the menu on the left, click on modules, then at the bottom of the list enable the module.
Then from the menu on the left again, click on OPC UA then add a new Opto22 device from the list.
Once to select it form the list, you can fill out the details:
From there, your PAC Control tags will show up in designer - Well… to be clear, the PAC Control tags that you have checked the ‘Public Access’ option on…
Be sure and have only the tags / I/O that you want to make public checked. There is no need to check every tag in the strategy.
Lets know if you get up and running.