Fetches required data from the shop, if needed, and creates a registration URL out of it. Usually these links are static, but they could contain information like affiliate data or tokens, if required. The URL should not expire, because it’s fetched only once in the default theme.
Returns the registration url.
An optional date-time-string in the format ISO 8601 (YYYY-MM-DDTH:i:s.fZ). The URL does not expire if this field is not set. The returned timezone is always UTC (+00:00)