Requirements for "bid to upgrade": works with codeshare?
I bought a ticket on VS metal with a DL codeshare (HSV-ATL-SEA on DL, then SEA-LHR-ATL on VS on the return). First leg is 90 days from today. When I try to use the "bid for upgrade" button, I get a message telling me that I can't. I haven't found any documentation around how these upgrades are parceled out-- is it based on fare class? Ticket issuer? Phase of the moon? My first thought was that because I bought my ticket on the DL website, and it's a DL codeshare, that I can't bid, but I don't know that for sure. Is this process explained anywhere?