You have set HappyPet up. Before you take real bookings, spend twenty minutes on this. Every item here is something that is annoying to fix later and easy to fix now.
Money
Check a few prices against what you actually charge. Prices copied in a hurry are the most common thing found wrong in week one.
Take one test payment and refund it, so you know the whole path works before a customer is standing there.
If customers pay you by bank transfer, check the account details character by character.
Your services
Book a test appointment for each service you offer. Not one, each. Services get set up for the wrong pet type or the wrong branch, and that only shows when somebody tries to book.
Delete the test bookings afterwards so they do not sit in your numbers.
Your team
Check everybody can sign in, on the device they will actually use. A password that works on the office computer and not on somebody's phone is worth finding out about now.
Check what each person can see. Somebody who can see more than they should is a problem you want to find before it matters, not after.
Messages
Send yourself every automatic message you have turned on and read them on a phone. Wording that looks fine on a computer often reads oddly on a small screen.
Check your business name is right in them. A message signed with a placeholder is not a good first impression.
Your pets and customers
If you brought customers over from somewhere else, open five at random and check the phone numbers have their country code. Numbers without one never receive anything, and you will not find out until somebody complains they were never told.
The day itself
Have somebody available who knows the system. The first day is when questions happen, and an answer within a minute keeps everyone calm.
Do not go live on your busiest day of the week. Pick a quiet one.