Enabling Twitter Cards on specific sub domain


How to Enable twitter card on specific sub domain?

Say example.com has two sub domains X1.example.com and X2.example.com.

How to enable twitter card only on X1 ?


Yes it’s possible.
In fact except if the subdomain is www, only the subdomain should be whitelisted by default (if the subdomain is www, all subdomains are whitelisted by default).
When filling the “Request Domain Approval” on the validator (https://dev.twitter.com/docs/cards/validation/validator), make sure that “Website Domain” is “X1.example.com” and not “example.com”.