If you’re sent a payment reminder but were expecting an invoice to be auto-paid, there was most likely an adjustment in the recurring invoice amount. Such increases/decreases in amount require that re-entry of payment information.
Most invoice emails will indicate such an adjustment:
IMPORTANT: Your subscription has changed to X hr/mo (was X hr/mo). Please re-enter your credit card credentials to authorize the price increase. Also, please check the box to "automatically pay" every month per TitleLeaf terms of service.