Based on what I've read here, it seems like Priceline/United has a bad customer interface that provides false information. I don't think it's intentional; it sounds more like the people who drafted the text don't understand enough about ticketing (or their own system) to appreciate that they got it wrong.

But OP is still right to be upset. And I don't buy the suggestions that it's at all OP's fault because if he's only clicked through three optional screens, or tried to assign seats, or asked for a briefing by UA revenue management before booking...

You should not need intimidate knowledge of fare codes or policies to book a vacation package.

And I don't object to holding United partly responsible for resolving the problem. They put their branding on this portal and clearly market it aggressively. They should make Priceline fix the problem and, in the interim, upgrade OP.