hmm, i’m not sure at the moment whether this is a custom domain issue or a page not found issue.
this is the process for resolving “another site is using this domain” type concerns:
If you have some idea of who might be using the domain (maybe a previous collaborator or an agency you’ve worked with in the past?), the quickest way to get this resolved is for you to contact that person directly and ask them to remove the domain from their account here:
Netlify App > “Options” dropdown > “Remove domain”
If you’re not sure, please verify domain ownership and let us know by responding here when that’s done. If the verification is successful we can remove the domain from the other account so you can use it on yours.