Page Managers can add twitter card meta data into the head by using the Google Analytics box.

The steps are as follows:
  1. Go to onMessage > Website and select the site to update.
  2. Select Site Settings.
  3. Scroll down to the Google Analytics: box.
  4. Add your twitter meta data at the bottom of the box.

For more information on Twitter Cards: https://developer.twitter.com/en/docs/tweets/optimize-with-cards/guides/getting-started
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