'The domain has been registered already' when adding a domain to Resend

Not specified by the original author.

TL;DR

Add that TXT record at your DNS provider to prove ownership. Common reasons: a teammate or contractor added it, or you are logged into a different account than the one that first added it.

Steps

1. Symptom: adding a domain in the dashboard fails with a message like "The example.com domain has been registered already".
2. Confirm the cause: this means the domain is active on a different Resend account. Common reasons: a teammate or contractor added it, or you are logged into a different account than the one that first added it.
3. First check: ask your team whether someone already uses Resend, and double-check which account you are signed into. The cheapest fix is using the account that already has it.
4. Fix via claim: on the Domains page, add the domain again and click Start claim when the in-use prompt appears. Resend gives you a DNS TXT record to add.
5. Add that TXT record at your DNS provider to prove ownership. The claim expires in 7 days, so do not let it sit.
6. If you previously started a claim, re-submit the same domain and click Continue claim to pick up where you left off.
7. Verify: once the claim completes, the domain appears in your account and you can add the normal sending records. If you cannot add DNS records, contact Resend support.

When to use

You are seeing this: Symptom: adding a domain in the dashboard fails with a message like "The example.com domain has been registered already". Use this skill when you run into "'The domain has been registered already' when adding a domain to Resend".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Documented in Resend knowledge base: a domain can only be active on one Resend account; the self-serve claim flow uses a DNS TXT proof record and expires in 7 days. Evidence: resend.com/docs/knowledge-base/domain-already-registered.