my Mamiya K/L lens want fit my RB67 Pro-s

I have purchased a 75mm K/L lens and it is supposed to fit both the RB67 and RZ67/RB67SD
That is what the K/L means, K for older RB67 and L for RB67SD and RZ67 series. And the lens fits my RZ67 but not my RB67 Pro-s. So according to what i have read i need to remove an adapter ring, but i just don't see it.

Oh i found it, but it's made in alloy. It was the senter ring. Here is a picture should anyone experience the same in the future