There are no payday loans in Australia who offer 100% guaranteed approval. Every lender has eligibility criteria, and while some have more relaxed rules than others, all lenders will reject applications from borrowers they see as too risky.
You should be very sceptical of anyone offering guaranteed approval.
If you don't make repayments on time you will be charged a fee. These fees are often flat payments which can add a lot to the total cost of your loan. Any defaults on the loan will also be listed as a negative mark on your credit report and can remain there for as long as seven years. If you already have a loan and you don't think you can make a repayment, contact the lender to discuss what your options are. Reputable lenders will work with you through processes such as payment plans.