Spotting the N1 に N2 construction (eg パンにバター）

Question

I have recently come to the conclusion that the N1 に N2 construction (eg パンにバター）is more common than I thought. It is the only explanation I think of to make gramatical sense of the sentences below. Could somebody confirm I have this right (in bold) in the following case?

なお、本状と行き違いにお支払い済みの場合はお許しください Please ignore this notice if you have already paid (this card and your payment have crossed)

Note

The following sentence has been removed as に should have been の：相手に言い分もわかったとはいえ、心から納得したわけではない ( "Although I understand were he's coming from, I can't really agree with him.")

Answer 1

It's not an instance of the listing に.

Here に indicates that (と)行き違い describes the manner in which お支払い(済み) was done.

Please forgive us in the case that payment has been completed "in crossing" with this letter. (=while the letter was still on its way... I'm not sure you can use this form for this in English, I might just have made "in crossing" up)

I think it's the same as this に, despite お支払い済み appearing not to be a verb...

And ringing the bell in passing, he led the way into the adjoining room.
そして通りすがりに鐘をならしつつ、かれは隣室へと一同を先導した。