If you have confirmed that you have admin access to a Facebook page, but it is still not being listed as an available page when making a Facebook Network connection, this problem may be related to Granular permission as described here:
People can grant app permissions for Pages and business assets they manage at the individual level. For example, someone who manages several Pages, may grant the app permission for only a particular page or for only some of the Page.
To check whether this is the case, go to your facebook settings (either Apps and Websites or Business Integrations) and click on ‘View and edit’ for the ContentMX app.
[Apps and Websites] https://www.facebook.com/settings?tab=applications
[Business Integrations] https://www.facebook.com/settings?tab=business_tools
In a window that opens, scroll down to the section “Show a list of the Pages you manage”. In this section, put a checkmark next to all of the pages you wish to access with the ContentMX app.