Line cant't be added to this account
I am currently having prepaid $10Unlimited Mobile Internet with up to 2GB of 5G & 4G LTE Data plan, but as I want to upgrade my plan into T-Mobile Prepaid Unlimited plan the alert is shown as "Line can't be added to this account" makes me unable to proceed to the next step. I do have sufficient fund in this account.Would like to solve this problem and upgrade my plan. thx