@Richard ****
that's not what the TDAC site says. It says country you are departing from ie where you are coming from. . Anyway, bear in mind if you put a transit airport as a country you've come from, there could be implications if it's on the yellow fever list. I've followed the TDAC advice and put the country I'm coming from, where I board my flight as per my ticket reference, as UK. The flight number is only for the plane you got off. My TDAC has been accepted and received the QR code in seconds. 😊