Hi rapidasia,
Thanks for reaching out.
There are two functions of Advanced Ads that require activation on the main page of your network. All other functions should also work if the plugin is only activated on the individual sub-pages.
Advanced Ads can create an ads.txt file on multisites automatically. In the backend of the main site of your network go to Advanced Ads > Settings > General > ads.txt. You should see the option to generate the ads.txt file for the whole network.
For more information on this see also ads.txt on multisites.
Second: The licenses could and should only be activated on the main blog in your network to allow updates. Normally, the Licenses tab on the settings page should not show up on subsites in your network. This affect automatic updates of the Advanced Ads add-ons.
If you have further questions regarding Advanced Ads, please let em know. If you want to ask more about the license activation, please reach out to me through our customer support.
Best regards,
Henning