If you don’t have enough money for a particular month, you should make a phone call or send an email to your lender. In most cases, lenders are more than willing to work with you so you don’t default on the loan. You may be able to work out a one-time partial payment or a payment plan that allows you to catch up over time.
A lender may also allow you to take a payment deferral, which means you won’t have to pay your loan for a month. While interest will still accrue, at least you’ll be off the hook for payment.