If, for ANY reason, payment isn't made by you on time we will attempt to collect from your secondary payment method and if this fails we will attempt to collect from from your guarantor in line with their agreement. This is beacuse it's important to make your payments in full and on time each month, as this is your contractual agreement and missing payments may damage your credit rating.
This is why it's really important that your guarantor trusts you to make your payments on time each month, that you agree that you can both afford to pay when needed and that your guarantor would be comfortable to pay on your behalf if something goes wrong.