There's the Google Pay service that processes payments.
There's the old Google Pay app that got rebranded as Google Wallet.
And then there's a newer Google Pay app available only in the US, Singapore, and India. This is the one getting shutdown.
See also: https://en.m.wikipedia.org/wiki/Google_Pay
And a very helpful chart: https://en.m.wikipedia.org/wiki/File:Googlepayments.svg