On this topic, does anyone know if you can buy up in the app beforehand or on the day at the airport from standard basic economy class (cheapest ticket) to Premium Economy on LEVEL? And if so, what the cost generally is for BCN-BOS? (I’m referring to the equivalent of what the BA board calls POUGs and AUPs)

What Avios do you earn? Can you only credit to the IB Avios program or can you credit to any of the other Avios programs too? I assume no BA tier points even if it’s booked with an IB code if it’s a LEVEL flight?