As per SEBI Regulations, settlement cycle for Derivative Segment (F&O) is T+1. If you have sold options, the premium amount will be realized on T+1 day only.

However, on T day i.e. the day you sold the option contract, this amount will not be considered as margin as it's not realised. So, if you open an F&O position, with the option premium received, you will be charged margin penalty by the exchange

Let's understand this with an example

You have sold Options and received a premium of Rs 50,000. Assuming you have ₹ 70,000 apart from this in your account, you bought 2 lots of NIFTY FUT in NRML at 1,20,000. Since the premium is not yet realised, while reporting your margins to the exchange, we'll not be allowed to report the option premium value. So you will be charged margin penalty on the shortfall amount of ₹ 50,000 (1.2 lacs - 70k)