Serve your lockers and links from your own hostname instead of ours. One DNS record, automatic SSL, and a trust bump that shows up in conversion rate.
By default your lockers and links are served from a platform hostname. A custom domain
puts them on yours instead, so a visitor sees go.yoursite.com rather than a domain
they have never met. On a locker, where the visitor is already being asked to complete
something, that difference is measurable.
Use a subdomain, not your apex. Something like:
go.yoursite.com
unlock.yoursite.com
links.yoursite.com
A subdomain keeps your main site untouched and can be pointed away again at any time without affecting it.
You cannot connect a platform-owned hostname or a subdomain of one. The domain has to be yours.
Go to Tools → Custom Domains and add the hostname. It is created in a pending state and the panel shows you the exact DNS record to add. That record is generated for your domain, so copy it from the panel rather than from any guide, including this one.
Add the record exactly as shown, then come back and press refresh.
If your domain is on Cloudflare, set the record to "DNS only" (grey cloud), not proxied. A proxied record puts Cloudflare's own edge in front of ours, and the certificate cannot be issued through it. This is by far the most common reason a domain sits pending.
DNS changes are not instant. A few minutes is typical, an hour is not unusual, and the panel keeps showing the record until it sees it.
Once the record is live, the certificate is issued automatically. No CSR, no upload, nothing to renew. The domain flips to connected and your lockers and links begin serving from it.
New lockers and links pick up the domain automatically. Links you already published on the old hostname keep working, so there is no flag day and nothing to migrate.
Work down this list; it is almost always one of these:
A domain connected to one account cannot be connected to another at the same time: hostnames are scoped per publisher, which is what stops anyone serving their content on your domain.