Just worked it out. Seems to be when I'm searching for work travel, with Bluebiz account selected.
And that's helpful, as makes for much more flex than our corporate travel partner.
A fare to to experiment with.
Monday April 17,
1750-2205
Vienna to Edinburgh, via CDG
Logged in via AF app
Fare lock in fee: 10 GBP
Guaranteed until 14 Feb (72 hours from now)
NO bluebiz
Logged in via KLM appFare lock in fee: 0 GBPGuaranteed until 15 April (exactly 48hrs before travel)
Selected Bluebiz for work travel
Logged in via KLM appFare lock in fee: 10 GBPGuaranteed until 14 Feb (72 hours from now)
No bluebiz