After I changed the blueprint yml file, It appeared when I tried to modify the page content.
This usually appears when there are multiple errors in the form, e.g. required fields not filled in, field content is not valid etc.
Without more information what exactly you changed it is hard to tell exactly.
Yes, After I removed the “preset: page” in blueprint, I can save it.
I get also get that error but don’t think it is related to a preset because I don’t have that in my blueprint.
- localhost
- macOS
- running from /Sites folder
Everything used to work until I downloaded everything from my server down to the local machine. So I assume some files are either missing or have wrong permissions. The question is: which ones are relevant?
I tried to do 777 on content folder which doesn’t fix it. I have a feeling it has to do with .lock files (maybe they got downloaded from the server as well and I don’t “own” them?)
Would like to understand what that error “Please fix all form errors" and the “PATCH” in dev tools mean. 
app.js:1 PATCH http://localhost/~fs/my-kirby-site/api//pages/stream 500 (Internal Server Error)
What I noticed is the “//” between api and pages…
Why do you think that? Then you should find .lock files in the page that doesn’t save.
What is your local environment?
Can you do other things in the Panel, like upload images, create pages etc.?
I figured it out: I forgot to add the router when starting the server… php -S localhost:8000 kirby/router.php Still not used to that change from Kirby 2 => Kirby 3 