Apple Pay: Is an unauthorized purchase attempt a scam?

Yes. Those types of messages are usually scams. Apple Pay requires, 1. Your devices that hold your payment method and 2. your biometric authentication (Face ID or Touch ID) to complete a purchase.

Also, apple will never hold up and confirm a purchase using Apple Pay via message or email. The purchase is either accepted or denied at the point it is made and does not generate a warning email for confirmation.

click here ➜ Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support

That’s a phishing attempt from scammers and it’s literally been reported 100’s of times if not 1000’s. 

Apple would never contact you. Your bank (issuer of card) would contract you. Banks do the exact opposite of the message you received. If they suspect fraud the transaction is stopped immediately. You have to call to verify the transaction, not call to stop the transaction. 

“Don't answer suspicious phone calls or messages claiming to be from Apple. Instead, contact Apple directly through our official support channels.”

”To report a suspicious SMS text message that looks like it's supposed to be from Apple, take a screenshot of the message and email the screenshot to reportphishing@apple.com.”

You can report phishing at these links and most importantly your local law enforcement.

Identify legitimate emails from the App Store or iTunes Store.

FTC Complaint Assistant

FBI’s Internet Crime Complaint Center

Learn about how not to be a victim of Social Engineering.

Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support

You’re welcome and I hope you have a great evening.

Your'e very welcome.