Good morning @Kristina347,
Thank you for reaching out to us here on the Community Forums. I completely understand the importance of being able to set up a payment with your online account. I would be ecstatic to help you with this endeavor.
Have you tried to login to your myAT&T account from a web browser yet? This would be the next step to determine if there is any kind of issue with your profile. If different people have access to the account with more than one login, you will want to make sure you are using the main access I.D. to access this part of the account.
We do have a great online support article which does go over how to successfully set up a payment arrangement through either a computer or mobile device. On the top of the page will be a drop down to select either Desktop/Tablet or Smartphone/myAT&T app to show you the correct ways to set up the arrangement depending on the method you prefer.
I hope this helps! If any questions should arise, feel free to let us know here on this thread and we’ll be happy to help! Have a great rest of your week.
Austin, AT&T Community Specialist