how do I set error logging?

Hi

I'm playing with CI4, I've used CI before years ago. I've gotten as far as 

https://df2.pennyjack.co.uk/index.php

and I'm getting: 

Whoops!

We seem to have hit a snag. Please try again later...

I cannot find error logs anywhere. I've swallowed hard and set the writable folder to 777 but still nothing.  How do I set/get the error logs?


Thanks