Is Circle Pay a reversible transfer service?
Just like the Neteller, Skrill and the rest of payment methods. If the account was funded using crypto, no, otherwise yes. I suggest reading the full User agreement so you know what you're getting yourself into:
Once a bitcoin transaction has been initiated, it cannot be reversed. Deposits using a bank account, debit card, or credit card may be reversed or may be subject to a chargeback or related claim.