Hi, @levgroup. The issue here is that the site without the custom domain is also a page not found:
$ curl --compressed -svo /dev/null https://monumental-bunny-1ac2cf.netlify.app/ 2>&1 | egrep '^(<|>)'
> GET / HTTP/2
> Host: monumental-bunny-1ac2cf.netlify.app
> user-agent: curl/7.79.1
> accept: */*
> accept-encoding: deflate, gzip
>
< HTTP/2 404
< age: 0
< cache-control: public, max-age=0, must-revalidate
< content-encoding: gzip
< content-type: text/html; charset=utf-8
< date: Thu, 14 Jul 2022 04:03:28 GMT
< etag: 1657749047-ssl-df
< server: Netlify
< strict-transport-security: max-age=31536000; includeSubDomains; preload
< vary: Accept-Encoding
< x-nf-request-id: 01G7XE0FDX7G9DPRDX55JVJ8FN
<
This support guide is the starting place for that: