DanielJS
It turns out that, depending on the region from where you have purchased the ticket, there is currently a technical glitch. The date of validity or date of birth is set to +1 day from the originally entered date.
Please get in touch with the SBB Customer Service to ask whether they issue a new ticket or if you will receive a confirmation to use the ticket with the wrong date of birth. You can use the form below to get in touch with the customer service, simply mention that you were instructed by the SBB Community to do so.
https://www.sbb.ch/en/help-and-contact/customer-service/praise-comments/reklamation-auswahl.html
Our community manager @RomanoS is in touch with the SBB Customer Service team concerning this bug.
Bascially, it is not an issue as long as the names are given as in the passport and the month / year of the date of birth is correct as well.
Kind regards,
Roland