Record conflicts
Most conflicts come from one source: records left over from wherever your domain was hosted or pointed before. Adding our records without removing the old ones doesn't always fail outright, sometimes it just breaks things quietly.
The main scenario: leftover records
If your domain was previously hosted elsewhere, especially with a website builder like Squarespace, Wix, or Webflow, chances are there are existing records at the exact same names we need: www and @. These need to be replaced, not added alongside.
www CNAME conflicts
Most DNS providers let you simply edit an existing CNAME's value, so this is usually straightforward. But some previous hosts (Squarespace, Wix, and similar) set an A record at www instead of a CNAME. In that case, you'll need to delete that A record first, a CNAME can't coexist with another record type at the same name.
Apex A record conflicts (the silent one)
This is the trickiest to catch. Previous hosts often leave one or more A records at @ pointing at their own IPs. If you add our two A records (188.114.96.9 and 188.114.97.9) without removing the old ones, the domain ends up resolving to multiple IPs at once, some visitors hit the old host, some hit Redirect Supply. Nothing errors, it just works inconsistently, which is a confusing thing to debug if you don't know to look for it. Delete any existing A records at @ before adding ours.
Don't forget AAAA records
If your previous host also set IPv6 (AAAA) records at @, remove those too. They cause the same silent traffic-splitting issue as leftover A records, just on IPv6-capable networks.
Setting up a subdomain over an existing record
If you're adding a subdomain (e.g. go.example.com) and that name already has an A record from a previous setup, delete it before adding our CNAME, a name can't have both at once. Some DNS providers will reject the add outright if you don't; others will let it through in a broken state.
CAA records
A CAA record from a previous host can also block our SSL certificate from issuing, that's covered in SSL Certificate Issues, worth checking there if HTTPS specifically isn't working even though DNS looks fine.