Lockbox and IRRoxdvlock box and IRR

Hi, I am buying an infrastructure asset and I have a question about the valuation and IRR

I am using XIRR to calculate the IRR and also the mid year convention. If the lock box date (where the economic interest is transferred to me) is 31 Dec 2019 and the closing date (where my money is actually transferred to the seller) is 30 September 2020, is it reasonable to assume the first cashflow I get is on 30 June 2020 and then the consideration I pay is on 30 September 2020?

It puzzles me because it seems like I get some cashflow before I pay the consideration?