The domain troubleshooting guide can help with most custom domain configuration issues. You might be able to use that guide to solve it before a human is available to help you. Then you can come back here and share the answer for bonus points.
You can also use v0 to narrow down the possibilities.
Since vercel alias works for a specific deployment but adding the domain in the dashboard says it is already assigned elsewhere, I’d check whether this is a deployment alias still attached in the same scope before assuming it is fully orphaned.
From the account/team that should own it, try:
vercel switch
vercel alias ls --limit 100
If lianxi.vercel.app appears there, remove the stale alias first:
vercel alias rm lianxi.vercel.app
Then try adding it again from the lianxi project’s Settings → Domains page.
If vercel alias ls does not show lianxi.vercel.app in your current scope, but the dashboard still says it is assigned to another project, then this is probably not fixable from the CLI. In that case the useful info for Vercel is:
Domain: lianxi.vercel.app
Target project: lianxi
Current team/scope: ali-zohairs-projects
Dashboard error: already assigned to another project
CLI alias works, but dashboard project-domain registration fails
I’d avoid posting tokens or private project IDs, but the exact domain + target project + error text should be enough for someone from Vercel to check whether the alias is stuck on a deleted or hidden project.