Symptom: SPF verifies but DKIM stays failing, with a red wavy underline on the DKIM value in the domain details page.
1. Confirm the cause: compare your DNS record against the value on Resend's domain configuration page character by character. The usual mistakes: extra quotes or spaces around the value, a truncated long value, or SPF information pasted into the DKIM record by accident.
2. Fix: copy the entire DKIM value from the Resend domain page and paste it into a single TXT record, replacing what is there. Do not retype it and do not split it across lines unless your provider requires chunking and reassembles it correctly.
3. Check the record name: the DKIM record typically lives at resend._domainkey under your domain. Confirm it with nslookup -type=TXT resend._domainkey.example.com and compare the returned string to Resend's value.
4. Verify: use "Restart verification" and confirm the underline clears and DKIM shows verified.