This code is based from this topic.
Ever since I posted this question, I’ve also tried to replace the ‘A’ and ‘B’ with the file name (i.e., ‘OrderA.xlsx’, ‘OrderB.xlsx’), as well as using coin flip under code component. None of which worked.
To summarise, what I’m trying to do is randomly assign a list (OrderA.xlsx or OrderB.xlsx), but not both, to online users participating in the experiment. This is my first time using PsychoPy, so any help would be appreciated! 
Thasya