ERR_DEBIT_MEMO on Xero: Debit memo error. Root cause: The debit memo is not properly formatted or has not been correctly linked to the original invoice or purchase order it is adjusting. Debit memos must reference a valid source document and adjustment amount must not exceed original transaction value. Step 1: Verify debit memo format and structure. Open debit memo and check all required fields are filled: Supplier name, Debit Memo number, Date, Reference to original bill/PO number, Line items with descriptions and amounts. Debit memo should have clear reference to source document it adjusts. If any field blank, fill it in before resubmitting. Step 2: Link debit memo to original bill or PO. In the debit memo, find "Links to" or "Related Document" field. Click and select original bill or purchase order from dropdown. Ensure the linked document exists and is active (not deleted or archived). The system will not accept debit memo without valid source document link. Step 3: Verify debit amount does not exceed original transaction. Compare debit memo amount to original bill amount. Debit memo amount should not exceed original. Example: if original bill was $1000, debit memo cannot be for $1200. If too high, reduce to correct amount. Debit memos can only reduce or adjust original amount, not exceed it. Step 4: Check line item descriptions and amounts. Review each line item on debit memo. Each should have: item description, quantity (if applicable), unit price, and total amount. Amounts should be negative (indicating reduction) or clearly marked as adjustments. Verify math: quantity × price = line total. Verify line totals sum to memo total. Step 5: Verify memo is for correct supplier and period. Confirm supplier name on debit memo matches original bill exactly. Check debit memo date is after original bill date (cannot backdate). Verify debit memo is in correct accounting period (not for closed month/quarter). If period closed, may need manager approval to post adjustment. Step 6: Apply debit memo to original bill. After all validations pass, go to original bill and look for "Apply Debit Memo" or "Link Adjustment" button. Select the debit memo and confirm. Original bill balance should decrease by memo amount. If memo fully offsets bill, bill status may change to "Adjusted" or "Closed". Document reason for adjustment in bill notes.