• Someone on your behalf created the account or you are using an Apple ID which belonged to someone else when you got the device.
• Sharing sign in credentials with family and friends. Remember Apple ID is a personal webmail service.
• Unable to recognize the Apple ID logged in your device.
• Shared password with someone else intentionally or unintentionally such as on phishing site, told someone etc.
• A weak password which is easy to guess or has been compromised.

How to re-access the Account:

• Log in to your Apple ID page. In case, if you are not able to log in or receive a message ‘account is locked’ then try resetting the password.  
• Change the sign in password and create it into a strong password.
• Go through all the personal and security details in the account. Update any information which you didn’t find right or unable to recognize. It includes name, primary email address, alternate email address, phone number, security questions with answers as well as the devices on which you are using the account.
• Also, check with the email address provider. This is because to ensure you have control on every address associated with the email ID.
• Apart from above steps, also set up two-factor authentication for your ID. This will provide additional security designed to prevent anyone to access email service.

You can also consult the team of Apple Pay Support Australia at 1-800-789-560 and they will help you with the procedure.

Follow the below instructions:

• Access the wallet app.
• On the right corner, click on ‘+’ icon and then select ‘Continue’.
• Tap on ‘Add another card’ if this option appears.
• Now, position the camera for letting the card appear within the box
• It might take some time but the app should recognize the card number and expiry date.
• On next window, the details will appear as automatically added. Check whether the details entered is correct and if not, amend it. Click on Next.
• On the next screen, you can check the Expiry date. From the back side of the device, enter the ‘3 digit’ security code.
• Apple will then contact your card issuer and accordingly will add your card.
• Now, agree to the ‘Terms and Conditions’ and wait till the device sets up the digital wallet for the card.
• The next step includes the verification of details entered and here you can select whether you want to verify by dropping a call to your bank or via text message. If you choose the second option, then the bank will message you a code.