Pipe characters are being stripped from the customer id when using the checkout iframe. This does not happen with the iOS or Android SDK so pipe should be supported.
https://test.chargebee.com/hosted_pages/checkout?subscription_items%5Bitem_price_id%5D%5B0%5D=miamigrandprix23_web-USD&layout=in_app&customer%5Bid%5D=auth0%7Cxs8saf8sdf7asdf87&customer%5Bemail%5D=michael%40test.com&hp_opener=chargebee&hp_referrer=http%3A%2F%2Flocalhost%3A3000&layout=in_app