If OTR_HTTPPREFIX hasn't been configured (via defaults file or environment variable), the url saved in a tour view contains a literal (null):

"url": "(null)/view/ea83c5a1-e8e5-4c82-8c1b-175e784a959e"

which results in iOS attempting to use exactly that.

I don't think there's much we can do about it other than slightly "beautify" that null by returning a URL as

"url": "OTR_HTTPPREFIX/view/24c6bbb9-17bd-4b7e-b244-a2da77cb866f"

as an indication that something needs fixing server-side.