Escalate late approvals, open follow-ups, remind reviewers. Every one is ready to run, and you can adjust it in plain language.
Prompt the next reviewer when an entered bill nears its due date.
Your next approver gets a reminder before the payment cutoff, with the follow-up recorded on the bill.
Put each unapproved bill due soon on the follow-up task list.
Get clear follow-up tasks for bills nearing payment, so your payables person knows which approvals to chase.