Could a VPN or proxy service cause a 'response code 403' error in Smart Tube Next, and how can I verify this?

Yes, a VPN or proxy service is a frequent cause of 403 errors. If the IP address assigned by your VPN/proxy is blacklisted by YouTube, or if you're attempting to access content that is restricted in the VPN's server region, the server will deny your request with a 403. To verify, temporarily disable your VPN or proxy service and then try playing content in Smart Tube Next again. If the error is resolved, your VPN/proxy was the likely culprit.