Originally Posted by jsloan

The lack of R on the domestic segment really shouldn’t be an issue; IME if you have two d ifferent fare classes on the two legs, the app will check each one individually,

That said, what you’re seeing is something that UA is apparently experimenting with — inventory restrictions based upon the origin of the itinerary. That flight is R1 for itineraries originating in Europe, but it’s A1 R0 for itineraries originating in the USA. It’s not a point-of-sake restriction, as UA bases its point of sale on the credit card billing address of the purchaser; I got different availability for the same flight based upon a one-way vs. the return flight of a round-trip. You don’t say as much form your message, but I’m inferring that this is a return leg.

You can see it yourself in Expert Mode if you pair any outbound flight today (Sep 2) to Paris with the return flight you’re attempting to book tomorrow (Sep 3).