Is there an unauthorized Apple Pay charge on my account?

You’ll need to call Apple at 1-800-MY-APPLE to verify the number. More than likely it’s a phishing attempt by scammers to obtain personal and financial information from you.

Please review the support article from Apple I shared below.

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

On what account?

Apple Pay is not an account. Apple Pay is a payment conduit. It uses your credit or debit cards added to the Wallet app on an iPhone or Apple Watch to make payments in physical stores, websites and some supported Apps.

Usually texts alleging charges like that are scams. Apple will never send a text regarding a charge through Apple Pay, because 1, they can't know you did not want to actually make the payment and 2, payments through Apple Pay require biometrical confirmation (Touch ID or Face ID or password).

Whatever that was, is most likely a scam.

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