Exactly. You're bookend in Economy (ouch) on both legs. It was a fare class miss mapping between the different reservation systems. You booked into economy but the LAN website is confused because it thinks R is business. R is actually Economy on your carrier.

Annoying yes, but it doesn’t change the fact.

Did you bother to check the fare rules during the booking process? These should have shown your actual class of service.

I also have to add, you probably knew you were in economy on both legs but hopping for a glitch that would get you a pass. The fare you quoted is obviously NOT a business class fare, even for only one leg on a highly discounted fare. I suspect you knew this and hoped you get away with something. You didn't.

Nice try though