This will remove the tag from all Contacts
This call will remove the targeted tag from all Contacts that have it.
To remove a tag for an individual contact, but not delete the tag itself:
Retrieve the "association id" with a GET call to /api/3/contacts/:contactId/contactTags,
Then delete that associate between tag and contact, here: https://developers.activecampaign.com/reference/remove-a-contacts-tag