There are basically two different support channels. {pve} itself if fully open source, so we always encourage our users to discuss and share their knowledge using the Community Support Forum. The forum is fully moderated by the Proxmox support team. Up to now, the forum has about 25.000 members, and more than 120.000 messages. Needless to say that such a large forum is a great place to get information.
The second channel is the commercial support provided by {proxmoxGmbh}. {pve} server subscriptions can be ordered online, see {pve} Shop. For all details see {pve} Subscription Service Plans.
Please contact the Proxmox sales team for commercial support requests or volume discounts.