Update Billing: Click "Billing" in left menu. Add your payment method here. If your existing payment method is failing, delete it and redo the new payment method. If you have set up multiple payment sources, select the one you want to use as "Default". Click "Process pending payments.
If your current billing is setup using Apple App Store or Google Play, you can move it to iPlum web portal billing: Dashboard || Users || Click iPlum Login ID of the User || Plans || Number Plan || Change.
Important: After you have successfully moved iPlum subscription to the web portal, you should cancel the subscription at Apple App Store / Google Play so that you are not billed twice. iPlum doesn't have access to your Apple App store or Google Play account for cancellations.
Reactivate a canceled number: If your number was cancelled due to any reason within last 30 days you can Reactivate it. by following steps listed at the FAQ.