Hello @matias.lynch ,
You might try to use an assign (testVar = “Login” + bej + “.xaml”) prior your invoke workflow file activity, and afterwards
Within the invoke workflow activity just pass the testVar.
It sounds strange, but sometimes it is worthy to separate the computation from the actual activity that you are using.
P.S. And do not forget to have the latest version of the used packages both within your workflow, and within your invoked workflow…
Hope this helps!
Best regards,
Marius