An unexpected error has occurred

Steam is having technical issues due to the following reasons:

• Some kind of a temporary processing issue caused by a hiccup on the Steam client’s or the server’s end.
• An IP proxy or VPN being in effect. The Steam store is programmed to decline any actions initiated while the client’s IP address is masked or spoofed.
• Steam servers being down.

How can you solve it?

• Retry redeeming your code.
• Disable any VPNs you have turned on.
• Wait for the underlying issue to be resolved.
• Contact Steam Support.