You need API key - you can get it in you account overview.
Theese are various tips on how to make space in your inventory.
Stack these items:
These items have incomplete stacks (less than 250 items) in multiple locations and should be stacked together to save up on inventory space.
Craft stack away:
You have more than stack (250 items) of ingredients for following items. You can craft theese items to reduce amount of stacks.