Hello Liemeembiesh40
Firstly, welcome to the SBB Community. We are a customer support forum run by volunteers.
You can purchase as many Saver Day Passes as you need, as long as the stock lasts, since the total number of Saver Day Passes available per day is limited to a certain number.
Without any screenshots or further description of the error message, we are unable to assist.
Also, we suggest creating a user account to purchase tickets.
Kind regards,
Roland