@Nate Mendenhall There was an issue with the new editor where it wasn’t possible to type in a custom value (the editor would only let you select from fields from other steps in the Zap) but that’s now fixed. I’m sorry for the hassle with that! You can now type a custom value for the page using the page ID.
In terms of the order of when you need to be given access and when you set up the Zap, you need to be given all of the relevant permissions before connecting the account to your Zap. If you add permissions after the account is connected to Zapier, you’ll need to reconnect it in My Apps.
@logier9 If you can see the page when you are setting up a Facebook Pages Zap but not in a Facebook Lead Ads Zap, that suggests that you don’t have Ad management permissions. Please could you take a look at this help guide that details each of the permissions that you need in Facebook: Facebook Lead Ads - What Permissions do I need? Don’t forget that you’ll need to reconnect your Facebook Lead Ads account in Zapier after you add any additional permissions.