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.