How do I fix this?

libraries/ArduCAM_ESP8266_UNO-master: no headers files (.h) found

I tried deleting and redownloading but that didn't work.

Please post a link (using the chain links icon on the forum toolbar to make it clickable) to where you downloaded ArduCAM_ESP8266_UNO-master from.

chain links icon. I'm lost already.

It's just an IDE message. "Invalid library found in ...."

This is what the chain links icon looks like:

This is a URL without using the chain links icon:
https://forum.arduino.cc/
This is a URL with it:
https://forum.arduino.cc/

If you were someone spending time out of your day to provide free help, which of the above two would you prefer? Of course, we're all perfectly capable of copy/pasting a URL to the URL bar of the browser, but it takes some extra effort. Some simply won't bother, and thus you'll be less likely to get a solution to your problem. You want to make it easy for people to help you.

If your web browser doesn't show the forum toolbar, you can use bbcode markup to linkify the URL. It looks like this:

[url=https://forum.arduino.cc/]https://forum.arduino.cc/[/url]

sevenoutpinball:
It's just an IDE message. "Invalid library found in ...."

I understand that. You're the one confused here, not me. If you want help, provide the requested information. If you don't want help, then stop wasting my time.

It wanted a URL when my issue was with compiler error from a bad library.

But thanks.