How to use a different data adapter for the subreport

I’m trying to use a different data adapter for the subreport than for the main report. From what I’ve discovered so far you have to set it to use another connection (figure 1) and have a parameter to retrieve the connection (figure 2). What I can’t figure out is what to put in the Default Value Expression to get the connection. What I found in a 2018 article is to use com.jaspersoft.ireport.designer.utils.Misc.getConnection("opal") but that isn’t working. The name of my data adapter is “opal”. I need some help figuring this out. I feel like I’m so close.