You need to buy using Margin product, not CNC. CNC is only for stocks in cash segment. Margin is for F&O and Currency.

Hi Atul,

You will have to apply for SGBs through your bank by logging in to your net banking. Click on the option "SGB", fill-up the form and provide the required details and the bonds would be credited to your... (More)

https://community.fyers.in/question/how-to-buy-sovereign-gold-bond-2021-22-on-fyers-platform-60a21dee594c4e253f2dec03?answerId=60d2cae2604d03e89c8c313753