There is instruction is Zoho Campaign for verifying DKIM.
To add record 521._domainkey.domain.com but it will change to 21._domainkey when I entered the record. Is that the same? I cant verify it in Zoho Campaign.
It is, at least as long as only the domain disappears. “521” should stay.
Whats your domain and post a screenshot of your record.
domain is blackandblue.tech
Looks all right to me
$ dig +short @sam.ns.cloudflare.com 521._domainkey.blackandblue.tech TXT
"k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDkSDnY/gzwzBaHoH3T/+/In3l5mh6+bMRhebukB1IDGe6pbsQkkTwBijXYgLYpXAJd2B5MbyugR4gUFeOdY3WSHJc4CRnYYyVJOHMcSKlpOi/A4Yx7f726XmxhoSiowZ0qG9eD8LjtTx3HIGHNQMKmiG3xMwt9+1SQXz4C1gijeQIDAQAB"