There is some documentation here in the Monetate KB,https://support.monetate.com/hc/en-us/articles/209324386-Built-In-Third-Party-Analytics-Integration

Dear Paul,Internal Marketing Channel Bucket is based on your Internal Domains you have set.The rules you have explained above are same and will not value add anything.Go through the Links to set up your Marketing Channels : https://marketing.adobe.com/resources/help/en_US/mchannel/marketingchannels.pdf and Add Paid/Natural Search to Marketing Channel Report? Thank YouArun

You can change your marketing channel rules and exclude paypal.com from referring domains. Unless paypal is genuinely linking traffic to your site, it can pretty safely be excluded from referring domains.Internal is usually session refreshes. For example, I visit your site and then go to lunch for an hour. When I come back, I click a link. Clicking a link starts a new visit, but the referrer was a page internal to your site, hence the internal marketing channel.