A zone hold means the domain was previous or is currently in an Enterprise plan that has locked it to prevent it being added to another account.
Have you acquired the domain today? Are you trying to add it to a new account? If so, make sure the current/previous domain owner removes the lock. Otherwise you’ll need to raise a support ticket so support can check who applied the lock.
The domain owner authorized us to register his domain in our Cloudflare account, he is waiting for us to put the correspondent nameservers in his registrar (IONOS), once we have registered the domain in CF.