ATT message says that the phone I recently activated won't work (Device: Samsung Galaxy S10)

I activated my new SIM this morning and paid the amount for the 25$ plan with 300$ upfront fee. It worked fine until 30 min ago. I received a message saying:

"AT&T FREE MSG: We're always looking for ways to connect you to what you love faster than ever before. That's why we are taking steps to upgrade our network. We're sorry, but the phone you recently tried to activate won't work. Don't worry, we can help you. Visit your local AT&T store (att.com/store) for more info."