Can someone answer this dilema for me.

We raise some purchase orders with a specific delivery date of 1st of the month, in order to get the goods to us on the 1st, some suppliers raise the invoice dated the last day of the previous month.

I have just had a discussion with one company who rightly say that they need to raise the paperwork on say 31st in order for it to get to us for the 1st, so therefore the invoice should be treated as the month it was raised.

The purchasing manager here says goods were ordered for say 1st March, delivered 1st of march so therefore payable as a march invoice.

Who is right???