Codeshare not bookable with miles?
 

Trying to book a flight on MF operated by AE. It's been a CZ codeshare the past few days with confirmed space.

Trying to book it now and was told no more space because codeshares not bookable with miles.. Is that true?

Sometimes yes, sometimes no. It depends is it made available to DL by the codesharing airline. E.g. AF codeshares are normally bookable, but AZ ones are not - as AF has codeshares available for mileage bookings, while AZ does not.

I'd tried to do something similar recently (booking a KLM or AF flight operated by CY) and was told the same thing by DL. It appears that the flight has to be operated by a DL partner (it has to be DL partner metal).

Most of the cases yes. There are instances where AF has a hard block and treats is as entirely their inventory for revenue and awards.

You can book "AF" flight HEL-CDG that is operate by Finnair using SkyMiles. Been there done tat

Recently?

Same for the JL flight CDG-NRT. It is bookable using DL SkyMiles, as long as it's done under its AF codeshare.

Over the past few years I redeemed SkyMiles on trips which included FB-operated segments on AF and AZ codeshares.

That said I am sure one cannot redeem SkyMiles on EY-operated flights under KL, AF, AZ, and OK codeshares (i.e. AUH-MLE OK3190, KL3916, AF3814, etc).

So, my conclusion is that it's possible to redeem SkyMiles on some SkyTeam airline codeshares operated by a non-SkyTeam airlines, but definitely not on any codeshare.

It's been YMMV on agent's saying that MF (non codeshare flights) show up as redeemable. They're a ST partner, so I'm just curious as to why the agents do not see it on their end?

I booked that flight with miles about 6 mo ago. I had researched a much longer connection at CDG and was very happily surprised (and didn't question it!) when the agent suggested the earlier AY-operated flight.