Per https://rbidocs.rbi.org.in/rdocs/content/pdfs/03MD11022016_AN.pdf, you would need to select the purpose code S0001 I.e. Indian Portfolio Investment abroad in equity shares under the purpose group Foreign Portfolio Investments.
The limit prescribed by the Reserve Bank of India is US$ 250,000 per financial year per individual. This limit is subject to change by the RBI and is available on RBI's website.
The RBI's liberalised remittance scheme allows Indian residents to remit money abroad for various purposes, details are available at https://rbi.org.in/Scripts/NotificationUser.aspx?Id=10192&Mode=0. In your account with Interactive Brokers, you can invest (shorting is not permitted) in stocks, ETF's, bonds and options listed on over 100 markets across 26 countries. Margin trading is not permitted.