I have seen availability for a couple of economy tickets to Amsterdam through United and then transferred my miles to Axis.
The transaction wasn't going through and when I called them, they tried booking from their end too but then told that there is no inventory. The first leg to Frankfurt was through Vistara and then through Lufthansa to Amsterdam. I was told that Vistara isn't actually available even though it was showing as available on the website. I then asked them to check alternate flights which all had Vistara in the India-Frankfurt leg. They all showed as available on the website but I was again told that there is no inventory for any of them due to non availability of seats in the Vistara leg.
I asked them to book any possible airline on August 31 or September 1 to Amsterdam or Brussels or Stockholm or Copenhagen. Again the same response. Mostly because almost all flights from India to these locations has a Vistara leg in them.
My miles are stuck with United now and I don't think I will be able to redeem them for my Europe trip. I don't understand why more than 10 options that I saw as available on their website actually don't have any availability.
