After challenging String unshift function (https://www.freecodecamp.org/challenges/manipulate-arrays-with-unshift), the next step is linking to shopping T-shirt (https://shop.freecodecamp.org/)…
Do I have to buy some T-shirt so that I could go on with next challenge?
Looks like a bug. You don’t have to buy anything. You can go back to the map and select the challenge after that.
I kept running into that wall as well. It was unnerving that the shopping challange wasn’t being marked as complete 
I suppose all you can do is skip it.
It’s been fixed. 
This should now be fixed. Your browser may still redirect you as 301 redirects are cached. This should go away soon.