The manual way
Follow-ups on your shoulders.
Another awkward reminder
Rewrite the same email. Wonder if you're being too pushy.
Payment status, unclear
Check inboxes and records to find out what's still overdue.
One more spreadsheet update
Keep dates, balances, and follow-ups in sync by hand.
Inconsistent client follow-ups
Busy weeks turn timely reminders into last-minute nudges.