WFSupport on "[Plugin: Wordfence Security] invalid security token"

Are you activating per blog or through the network > plugins page (I think this may be only way but want to be sure I ask)? You might actually have to remove the plugin and re-install but follow this guide to do so.

https://wordfence.freshdesk.com/support/solutions/articles/1000010321-how-can-i-remove-all-wordfence-data-or-reset-wordfence-to-the-default

Tim