Onsdag

Try removing the rot from the input slot. It looks like you filled up the barrel, saw that the input slot was still empty, and so tried adding another stack of 64. When you add rot into a barrel it will automatically disappear from the input slot and fill up that blueish-grey bar instead. Once the grey bar is filled up you can seal the barrel. Adding more rot to the barrel, as you have done (stack of 64 in the input slot), is not necessary and will show up as 2 stacks of 64 in the output section. See attached image.