question

An unload activity expects a value for a destination. You can evaluate a token.label or you can select by sampler tool looking like an icon of an eye dropper directly in your model for your value of label destination.

You get a label value back by calling its name. I assume you gave the name like destination in Assign Label activity. This name is of datatype string. It is case sensitive. It DOES matter if you had given destination or Destination or you misspelled it in some way. You have to read the label value by calling the right exact name.
In unload activity you insert from picklist menu Label > your given label name OR you write directly token.destination. Or how you have called this label.

A personal advice: If an exercise does not work first, build it anew. Finding an error is a bit tricky. At later exercises authors expects you know facts of previous exercises. If you left some out, you won’t know what you should have learnt by then.