Putting www. in front of my domain makes it "unsecure"

putting www. in front of my domain makes it “unsecure”, and it redirects me to 000webhost saying that the domain is not used. my domain is https://peopleinspace.000webhostapp.com/ but if i go to www.peopleinspace.000webhostapp.com/ i get this:

Any ideas how to fix this?

Hello. Free domains don’t support www in front of them. We advise you to link a custom domain to your site, as they support it.

Likely cache related, try Incognito or InPrivate tab, failing that try CTRL F5, flushing browser data or another browser.