ERR_INVOICE_OVERDUE on Stripe: Invoice overdue. Root cause: The invoice has passed its due date and the system enforces overdue handling rules preventing further processing. Some systems automatically apply late fees, change status, or restrict modifications until balance is settled or payment plan agreed. Step 1: Verify invoice due date and status. Go to Invoices > Invoice List. Search by number or customer. Click to open and check Due Date field. Compare to today. If past due, invoice is overdue. Check Status field — should show "Open", "Overdue", or "Awaiting Payment". If "Paid" or "Closed", already settled. Step 2: Check for automatic late fees. In Settings > Company Settings > Invoices, check if automatic late fees enabled. If on, system may have added charge. Review invoice line items for "Late Fee" or "Interest Charge" line. If added, verify amount per customer agreement. Step 3: Contact the customer to collect payment. Send payment reminder including invoice number, original due date, current amount due (including late fees), and payment methods accepted. Offer brief grace period (3-5 business days) if policy allows. Include online pay link if available. Document contact attempt in notes. Step 4: Process the payment when received. When customer pays, record payment. Go to Invoices > Receive Payment, select invoice, enter amount and date. If partial payment, record what paid and leave balance open. If full amount including fees, mark as Paid. Step 5: Write off invoice if uncollectible. If customer disputes fees or refuses to pay, write off as bad debt. Create credit memo for disputed amount (including fees). Apply to invoice to reduce balance to zero. Document reason in notes. Prevents invoice from staying "Overdue" indefinitely. Step 6: Adjust invoicing process to prevent future issues. Implement automated payment reminders: 5 days before due date, on due date, 5-10 days after. Enable in settings. Review payment terms — if many pay late, shorten terms (Net 15 vs Net 30) or offer early payment discount (e.g., 2/10 Net 30).