I am a Delta Platinum Medallion, so I qualify as Sky Team Elite Plus.

I am flying into AMS from the US on a Delta-operated flight, and then connecting in AMS to OSL on a KLM-operated flight. According to both the Delta and KLM sites, as Sky Team Elite Plus connecting between flights operated by Sky Team partners, I am eligible to enter the KLM lounges in AMS.

I know I have to make my way from non-Schengen to Schengen to connect, but the layover is over eight hours. I was looking to book one of the sleep cabins in the non-Schengen KLM lounge to take a snooze for a few hours, and then move over to Schengen.

When I go to the KLM Lounge site to book the sleep cabin, and enter my ticket number, I am told "You are not eligible for lounge access with this ticket." After both calling and texting, nobody at KLM could tell me why the site says that - they agreed that I should have access, but their best advice was to just make my way to the lounge when I arrived in AMS, and try to book the cabin then.

I have no idea if these cabins are in high demand, so I was hoping to reserve ahead of time, just so I didn't show up day-of to be told "all the sleep cabins are booked, unfortunately."

Since no one at KLM is able to help, I was hoping someone here had first-hand knowledge that would be useful. Any thoughts? Is there a legit reason the site might be telling me I am not eligible for lounge access? Or should I chalk this up to a glitch?

Please and thank you!