How do I ensure that I have enough balance in my Upstox MF account?

There is no minimum balance that you have to maintain in Upstox MF account after the first time that you purchase the SIP.

After that, the regular SIP amount will be directly deducted from your bank account. So make sure that your bank account has the required funds. Otherwise, the order won’t be placed on that day. Upstox will try two times to deduct the amount from your account during one SIP interval.