Mobile Billing Purchases

I am an AT&T Customer and I am trying to figure out how to enable Mobile Billing to my Google Play Store account.....everytime I call AT&T they act like they don't know what I am talking about even after ive explained it multiple times and in different ways that I know best of how to explain "Mobile Purchasing"......Nobody seems to know how to help me out on this.....can someone on here help me with adding it...or tell me if my phone is capable of it?? I have the Samsung Galaxy A71 5G phone....it does give me the option when I go to adding a payment method...I click on it and then click on Enable...It comes up with an error message telling me that "Your AT&T account can't be used for mobile payments. Please select a different payment method or contact AT&T." So what do I do from there since AT&T reps don't seem to know what to do or what it is?? Even tried going to a local store and still no luck...