The forum's ticketing site also sells Boundary Zone fares.
Is this correct?
On the forum's ticketing site (my normal site of choice for buying tickets) I've tried to enter "Boundary Zone 6" (which is what you can enter on brfares.com) but it doesn't seem to be an option. Maybe it's called something else, but I can't work out what to enter. What it does do is allow you to enter as an option that you have a TFL 60+ oystercard. But unfortunately the forum's ticketing site appears to fail to offer the cheapest fare when doing this.
To give an example:
A return trip on a weekday after 9.30am from St Pancras to Leagrave using a Senior railcard with TFL 60+ Oyster.
brfares.com suggests that the cheapest fare is £9.60 (i.e. Boundary Zone 6 to Leagrave off-peak day return):
https://www.brfares.com/!fares?orig=0072&dest=LEA&rlc=SRN&period=20231001
But on the forum's ticketing website, it gives the cheapest option with Senior railcard and TFL 60+ oyster as £11.80. The ticket it offers at this price is a West Hampstead Stations to Leagrave off-peak day return. It is not clear to me why it is offering a ticket from West Hampstead - which is in Zone 2. The last station in Zone 6 is Elstree and Borehamwood. It seems that the site is not offering boundary fares and in addition is not offering the cheapest fares for journeys with TFL 60+ oysters.
As suggested by others, the c2c site does offer the correct cheapest fare of £9.60 (and allows Boundary Zone 6 to be entered as an origin/destination). I cannot find any other online ticket seller site that offers this. But c2c does seem to prove that it is possible to offer this ticket online!
One other observation is that the c2c option is TOD only, with no eTicket option (St Pancras to Leagrave is certainly an eTicket enabled route).
So far, my conclusion is that if you want these fares that you have to either use the c2c website or buy at a ticket office.
Be interested to know if others concur with my conclusions, or whether I'm making a mistake or missing something.