For those who wonder how the ForEach loop needs to be set up, you need a temp variable and a final variable.
Make sure that the ForEach is set to sequential or the content of your variables will be totally random!
This is how I set up my first (final) variable. In my case I used a semi colon as a separator since my items are email addresses.
The second variable is the temp variable that will temporarily keep the value until the next iteration, as because ADF just doesn't allow a variable to reference itself :(.