Ensure the code is being added through the Text Editor, as opposed to the Visual Editor. 

If the code is being added with the Text editor and is still being stripped, this indicates your user in WordPress does not have the Super Admin role. The Super Admin role allows additional functionality, like saving embed codes or script codes within the Text editor. 

To become a Super Admin:
  1. Request an existing Super Admin log in to WordPres
  2. Navigate to My Sites>Network Admin>Users
  3. Locate the user to upgrade and click Edit
  4. Mark the box for Super Admin
  5. Click Update User