So apparently these playoff games are not on ESPN+ , only on ESPN IF you have a tv subscription. From a cable cutter perspective - this is so stupid.
Yeah they sure don't make it easy for fans to purchase and access the product.
If you're interested in viewing the games after they've already aired - the ESPN+ service typically uploads them and makes them available within 24-36 hours of their initial airing. I'm using their app for access.
I just checked and Game 2 of NYR/WSH series is now available - I tried the MSG feed and it worked (going to watch the game in full later tonight)
If you ever get that prompt asking you to choose your cable provider for an already aired game that should now be uploaded/accessible on their service - try logging out of your account and then back to resolve the issue.