Every time a project is saved, activated, or deactivated (paused) we send a request to our server to build a new script with the new settings. We also send a request to our CDN provider to do a cache release for your visitors to get the updated script. To ensure that this cache release happens as fast as on your main website (the one you entered when creating the website in the Symplify UI) you need to enter all your other domains.
This is done in website settings. Click My websites -> click website to open the menu -> choose Edit website. Then enter all the domains you have the same script for comma-separated. See the example in the placeholder. Click Save when you are done.