Puly caff / cafiza if you can get hold of it conveniently, if not a crushed up dishwasher tablet is the same thing.
Edit, sorry did you mean de-scaling? If so citric acid or appliance descaler. If it’s aluminium inside you need tartaric acid or Gaggia descaler sachets.
What do I use to clean my wilfa classic coffee maker? It’s due one soon and I can’t find specifics online. Any ideas?