Why does it say update failed everytime i try to update to the new ios

What model iPhone? What version are you currently running?

Do you:

1. Have 6GB of free space?
2. A good WiFi connection (or a good 5G connection with limitations turned off if you have an iPhone 12).
3. Not using a VPN.
4. No beta profile on the phone.
5. At least a 50% battery charge and preferably connected to power.
6. Low Power mode turned off.