Common mistakes

2 min read · Chapter 7 of 8

What usually goes wrong

Symptom	Likely cause	Reversal path	Who absorbs it
Supplier says it wasn't paid; the bank shows the payment left	BEC: bank details changed after a spoofed or compromised email	Recall through the bank within hours; IC3 report; callback before any re-pay	The buyer, which still owes the supplier
Same invoice paid twice	Duplicate vendor records, paper plus PDF, a renumbered invoice, paying from a statement	Ask for a credit or refund; recovery audit	The buyer until recovered
Exception queue grows every month	No receipt entered, price variance, closed PO, tight tolerances	Receipt reminders, tolerance review, supplier credit memos	Supplier (DSO) and buyer (lost discounts, fees)
Discount offered, never taken	Approval slower than the window; run cadence	Faster routing; discount-priority runs	The buyer (about 37% a year forgone)
Late fees and a supplier credit hold	Invoice lost at intake or stuck with an absent approver	Pay with contractual interest; fix routing and delegation	The buyer; US federal buyers owe Prompt Payment interest
Check cashed by someone else, or amount altered	Mail theft, washing, counterfeit	Positive Pay return before the cut-off; bank claim; reissue	Banks by warranty, or the buyer if it declined Positive Pay
Supplier refuses the virtual card or adds a surcharge	Card fee above its margin; not enrolled with that issuer	Fall back to ACH; enforce any no-surcharge clause	The buyer loses the rebate or pays the surcharge
Wrong 1099 or a backup-withholding notice	Missing W-9, TIN mismatch, wrong threshold year	TIN Matching before filing; corrected return; withhold 24%	The buyer as payer
ACH returned: account closed or invalid	Stale vendor master	Fix the record, re-validate, resend	Buyer (ops, lateness); supplier (DSO)
Approval bottleneck at quarter end	Non-PO invoices with business approvers; delegation gaps	Delegation rules, escalation, PO-backed buying	Supplier first, then the buyer
Canadian input tax credit denied	Invalid GST/HST number or missing invoice fields	Registry check at intake; corrected invoice	The buyer
Supplier finance program withdrawn	Funder exits after terms were extended	Renegotiate terms; find liquidity	Buyer (cash cliff) and suppliers that relied on early pay

Supplier says it wasn't paid; the bank shows the payment left

Likely cause: BEC: bank details changed after a spoofed or compromised email
Reversal path: Recall through the bank within hours; IC3 report; callback before any re-pay
Who absorbs it: The buyer, which still owes the supplier

Same invoice paid twice

Likely cause: Duplicate vendor records, paper plus PDF, a renumbered invoice, paying from a statement
Reversal path: Ask for a credit or refund; recovery audit
Who absorbs it: The buyer until recovered

Exception queue grows every month

Likely cause: No receipt entered, price variance, closed PO, tight tolerances
Reversal path: Receipt reminders, tolerance review, supplier credit memos
Who absorbs it: Supplier (DSO) and buyer (lost discounts, fees)

Discount offered, never taken

Likely cause: Approval slower than the window; run cadence
Reversal path: Faster routing; discount-priority runs
Who absorbs it: The buyer (about 37% a year forgone)

Late fees and a supplier credit hold

Likely cause: Invoice lost at intake or stuck with an absent approver
Reversal path: Pay with contractual interest; fix routing and delegation
Who absorbs it: The buyer; US federal buyers owe Prompt Payment interest

Check cashed by someone else, or amount altered

Likely cause: Mail theft, washing, counterfeit
Reversal path: Positive Pay return before the cut-off; bank claim; reissue
Who absorbs it: Banks by warranty, or the buyer if it declined Positive Pay

Supplier refuses the virtual card or adds a surcharge

Likely cause: Card fee above its margin; not enrolled with that issuer
Reversal path: Fall back to ACH; enforce any no-surcharge clause
Who absorbs it: The buyer loses the rebate or pays the surcharge

Wrong 1099 or a backup-withholding notice

Likely cause: Missing W-9, TIN mismatch, wrong threshold year
Reversal path: TIN Matching before filing; corrected return; withhold 24%
Who absorbs it: The buyer as payer

ACH returned: account closed or invalid

Likely cause: Stale vendor master
Reversal path: Fix the record, re-validate, resend
Who absorbs it: Buyer (ops, lateness); supplier (DSO)

Approval bottleneck at quarter end

Likely cause: Non-PO invoices with business approvers; delegation gaps
Reversal path: Delegation rules, escalation, PO-backed buying
Who absorbs it: Supplier first, then the buyer

Canadian input tax credit denied

Likely cause: Invalid GST/HST number or missing invoice fields
Reversal path: Registry check at intake; corrected invoice
Who absorbs it: The buyer

Supplier finance program withdrawn

Likely cause: Funder exits after terms were extended
Reversal path: Renegotiate terms; find liquidity
Who absorbs it: Buyer (cash cliff) and suppliers that relied on early pay

Ranking these by volume or cost needs an operator's data; I haven't found any public.