Hello Devansh
Please contact SBB by phone: +41 51 225 78 56 (24/7, waiting times may be possible).
The Swiss Half Fare Card has to be valid earliest on the first day of travel in Switzerland, not before. It is not necessary to have an active Swiss Half Fare Card in order to purchase tickets. The system does not check it, it simply sells what you request. The only person being interested in your Swiss Half Fare Card is the ticket inspector.
Please, never share tickets details on the web. Protect them as you do with your personal information.
Kind regards,
Roland