Ah, as above. Sounds like it's changed.
Great tip, here: https://www.northstandchat.com/showthread.php?389466-Brentford-away-tickets&p=9980906&viewfull=1#post9980906
The site said we didn't have enough points when I first put them in basket, but I refreshed and all was fine.
I think they went on sale this morning slightly before 9am when the loyalty points unlocked.
If that ever happens to someone, don't panic - the ticket(s) is in your basket, and you...
I didn't know they'd gone with mixed coloured seating. I've been an advocate of that since I saw it in Portugal in 2004. Makes it much harder to spot unsold - or vacated - seats.