Lookup a SharePoint list based on another field value.

Though it's difficult to say what's going on without any other info of the values from your list, I would say that a little sanity checking could go a long way in your case.

Because your original lookup() function syntax is correct, the first thing I would do is check to see what happens if you were to just manually enter the string of said Department into your arguments like: 

That should get you *something* back. If it does, then you know your problem is somewhere to do with the reference to the value of your {Dept} Control.

If you get NOTHING back, and you know that it *should* be valid, then it's time to start digging a bit deeper.

The next questions are:

1. Is the Target List ("DivDeptLookup") on the same Site as the Form?
   
   
   
   1. No: Then you need to add the relative url path and a pipe delimiter before the target List Name, like: "/sites/siteCollection/siteA|customList"
      
      
   
   
   
   


2. What are the *actual* Column Names of the Columns that you're targeting?
   
   
   
   1. Go to the list in question
   
   
   2. Go to List Settings
   
   
   3. Click on a Column Name
   
   
   4. Look at the end of the URL (as detailed here: https://community.nintex.com/t5/Nintex-for-SharePoint-Forum/Need-to-Look-up-items-from-same-list-and-return-back-on-data-on/m-p/205140/highlight/true#M78432)
   
   
   
   

Try going through this list of possible solutions and if none of them work, then we'll dig a little deeper. Hope this helps.