I have an error code of 4000 does anyone know what it means

Where exactly are you seeing this error code? What computer OS are you using? The next steps would be to check that you have the latest version of iTunes installed on the computer. Or, are you attempting to update the phone OTA? If so, see this. Get help with over-the-air iOS updates - Apple Support

I've never seen that error number, and it is not listed in the support documents. I would say wait here for a bit and see if anyone else responds, or you can contact Apple Support. Is this error on the phone or the computer? Do you have any special anti-virus software on the computer? Can you try temporarily disabling it, and/or the firewall and try updating? Then you can turn that back on again.

I still cannot find anything. I asked earlier about anti-virus software, and/or Windows firewall. Not sure if either have tried to temporarily disabling them. If you have and still receive the error, I would recommend contacting Apple Support. I am not aware of any additional troubleshooting that can be tried. Make a Genius Bar appointment at the nearest Apple Store, or contact Apple Support about possible mail-in service.

Make sure that you have the latest version of iTunes on the computer (12.7.3). Otherwise, I'm not sure of any other troubleshooting step.

I am seeing this problem also on my iPhone 7+ and iPad Air after trying to install the latest update. I both devices are connected directly to my Windows 10 PC via USB. iTunes and Windows are both up-to-date. I have cold started the PC and the iOS devices to no avail. I would appreciate any help.

Thanks.

Where are you seeing the error, on the phone or the computer? That may help someone track the issue and come up with troubleshooting steps.