What is error 4000? I haven't been able to update my iphone for months.

Hi DnvrWrtr,

Welcome to the Apple Community, where some of us do our best to help each other.

There is another discussion thread that seems to provide an answer and a solution:

https://discussions.apple.com/thread/252878624

You may want to view the "Related Article" from that discussion thread:

"If you see an error when you update or restore your iPhone":

https://support.apple.com/en-us/HT201210

Hope this helps you :)