FAQ : Connectivity (Tunnels and Subnets) : Why are some PoPs not available for tunnels
Why are some PoPs not available for tunnels
All PoPs are regional, which means they only serve a specific region. This is determined amongst others by the country of your tunnel endpoint, BGP proximity and prefix filters. As such, when a PoP doesn't show up, do not change the country of your endpoint to force the PoP to show up anyway, doing so will cause your tunnel request to be rejected.
Additionally, some of the SixXS PoPs have a closed policy. If you want a tunnel on them you should contact the owner of the PoP and request them to grant you access, after which you will be able to select it as a preferred PoP. One can request such access by sending your request to SixXS who will relay your message forward.