Set up Wordfence on Multisite
Using Wordfence on Multisite
Wordfence should be installed as the network admin, and not on each individual site. See the Multisite section of the Wordfence System Requirements for more details.
API Keys for Multisite
If you want to use the paid version of Wordfence, you normally need one API key per WordPress installation. However, if you run WordPress Multisite, you only need one API key for the entire Multisite installation.