Washing machine pulley rocking on back of drum

Morning all,

Our Ikea integrated washing machine was making a knocking noise when the drum was turning.

On removing the back, I've discovered that it's the pulley knocking against the back of the drum.

It's almost as if the bot isn't tight, so it's not keeping the pulley hard up against where it's met the drum.

I removed the bolt, and and looked at the pulley, nothing appears to be missing, although I note on replacement pulley kits, theres a large washer and a smaller washer - I only have a larger washer.

This is the pulley I have

https://www.amazon.co.uk/AEG-WASHING-MACHINE-PLASTIC-PULLEY/dp/B084C3S7JB?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&psc=1&smid=A3MYEF0XBKZGAV&gQT=1

The rocking of the pulley is causing a knock as it rattles, and also causing the belt to slip towards the back of the pulley and its occasionally falling off.

Is it normal of the pulley to act loose?

Thanks in advance.