Good news to all TM UniFi users who wish to pay your monthly UniFi bill automatically with your credit card. I just discovered that you can now register for this autopay service online, don't even need to fill up and submit the paper form anymore.
Step 1: Login myUniFi Online Customer Centre (a.k.a. UniFi Customer Portal) with your myUniFi account.
Step 2: Once login, go to the myProfile tab.
Step 3: Click the Change Payment Method button.
Step 4: Fill in the online form and click the Save Changes button.
You can find a new service ticket is raised in mySupport which is immediately closed. Your payment method in myProfile should be updated as well.