Polini evolution - Vespa PK50XL2 problem

Hello,

 

I have bought new polini evolution exhaust on SIP. And this exhaust dosn't fit. do i have to by dedicated outlep pipe?

I have malossi 136 direct inside

 

Itis written that this exhaust fits to pk 50 xl2?

 

Could you explain me why?

 

Than You