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.
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.