Purchase Order with price zero

Hi expert.

I would like to know whether it is possible creating PO with net price = 0.

It is required to create PO with net price = 0 when running ME59N.

However it appears to be difficult because the system gives me messages saying "Net price must be greater than 0".

when creating POs in ME21N.

Or, is it possible flagging "free item" or unflagging "invoice receipt indicator" automatically when running ME59N?

Any help is welcome.

Best regards

Takeshi