What is it?. I thought charge card = never purchase APR.
The AMEX Charge Cards have the ability to delay payment on some balances, using features such as Pay Over Time. If the cardholder does not pay the entire balance by the due date, and AMEX allows balances to go into the Pay Over Time bucket, then the balances that are in that Pay Over Time bucket will be charged interest at the stated APR. The APR used may be the APR assigned to this cardholder, or it may be a promotional APR including 0% which AMEX has offered me on two charge cards, to encourage trying out the Pay Over Time feature.
Interest charges on a charge card are allowed. Even though the typical intent with a charge card is you pay it off monthly, it's still borrowing and can still be processed to charge interest costs. There is not a stated Credit Limit for the Charge Card, because the approvals of charges by AMEX are more dynamic for each cardholder, as compared to typical Credit Cards with a stated Credit Limit which the bank has to formally state any changes to that credit limit.