Issue was, i didn't quite grasp the concept of inventory space.
Reason why i couldn't claim the item was because my Inventory was "full", meaning i didn't have any slots left for new items.
The weird number that represents your inventory space (20k something) confused me quite a lot. probably the max amount when you hold 99x stacks in every slot?
Because the number didn't increase when i picked up items, i thought materials do not use inventory space, only equipment.
I think it would be a lot more self explanatory, if the number just displayed your used up inventory slots..