In detail
The portal FAQ says the Webfile uploaded for an appointment booking must not be older than 30 days. The portal does not accept a Webfile older than that.
Our reading: the FAQ does not say up to which date the 30 days are counted. We read it as the age on the day of upload: from the day the Webfile was generated to the day you book, not to the appointment date. That is our interpretation, not a written rule.
Here is where the limit bites: generate the Webfile far ahead of booking and the 30 days may run out; generate it at the last minute and you are rushing inside the 15-minute booking window. Generating it close to the day you expect to book, but before it, is sensible. That too is our advice.
If you fail to secure a slot, every uploaded Webfile is deleted from the system and you upload them again. The FAQ does not say whether the 30-day clock restarts then, and we do not assume it does.
The prep sheet has a small calculator for working this out from dates. Neither date is saved anywhere.