The yarn you use for Kniterate needs to be wound on a cone-shaped cardboard or plastic bobbin. The cone shape helps to unwind the yarn evenly while knitting. Yarn that is wound into a cake, like for domestic knitting machines, are not suitable for Kniterate.
Cylindrical plastic bobbins are mostly used for dyeing yarn and can cause issues during the unwinding when used on the knitting machine, like the yarn swinging in a larger radius, getting caught at the bottom more often or the outer layer of yarn simply sliding down the cone.
It is important that the yarn is wound evenly on the cone, especially if you use your own winder. This makes sure the yarn unwinds correctly while knitting, as irregularities could cause problems like yarn breaking.