SilverStripe 4 custom error page not shown

In my last project on SS 4, I’m trying to create my usual custom error pages – with same approach used on v. 3:

• Creating ErrorPage.ss inside /themes/mysite/templates/Layout;
• Including $Content inside template;

After a successful /dev/build?flush=all I don’t see any content, neither right template (I see the default Page.ss one instead).

In back-end there are error pages saved and published. In /assets/ there are the static ones too.

Maybe the procedure is changed in this new version? Any advice?

Thanks in advance everyone.

Answer

Your ErrorPage.ss folder structure needs to match the core PHP class’s namespace (SilverStripeErrorPageErrorPage), i.e. themes/mytheme/templates/SilverStripe/ErrorPage/Layout/ErrorPage.ss