Can I use my existing Indian Groww balance to fund my US account?

No, Groww balance can be used for Indian stock and mutual fund investments only, and not for US stocks. Since this is an international wire transaction and the account is being opened at Groww’s US-based broker partner’s end, your funds have to be directed under the LRS process before you trade. However, you are funding your own brokerage account from India to invest in US stocks. You could consider this as your USD balance.