Without an ABN, unless you provide us with a Statement by a Supplier, the ATO requires PetCloud to withhold 47% from your payments and remit them to the Tax Office. This is called the no-ABN withholding rule. Applying for an ABN is free. The Benefit - you are eligible to claim pet sitting and dog walking related tax deductions for allowable expenses you acquire in creating an income.
So if you plan on "carrying on an enterprise" Then you may need to get an ABN. If you are doing it as a hobby, then you may not need one. It is not compulsory for businesses to register for an ABN.
Refer to the ATO's website if you have questions about whether you are running a Business or Hobby.
It is important to keep all your receipts for expenses you wish to claim, and manage your business affairs properly (this means lodging any reporting and payments on time to the ATO and keeping good records if applicable). Talk to your accountant or a tax expert if you need to. The ATO Personal Tax Info Line 132 861 or the Small Business Info Line: 132 866.