I set up IPTV on Firestick. It worked fine at my friend house, but when I tried it at home, I got error code 456.
ISP is blocking you. You need to use a VPN.
Is there no other solution than using a VPN?
Yes, you can subscribe to your friend's ISP.
I think Urban VPN and Proton VPN are free. Check them out.
Can you recommend any paid VPN services?
I've used many of them. The best thing to do is start with a free one, use ProtonVPN for a while. Then maybe switch to NordVPN, OpenVPN or ExpressVPN. There are many options, such as Mullvad, IVPN, etc.
I think you should contact your provider. Explain the situation. They will either give you a playlist from a new server or add a VPN to your server. Be sure to consult your provider before paying for a VPN.
I am receiving error code 400. Will using a VPN resolve this?
Contact your provider directly. The problem is probably with them.