A cross-border payment is checked against restricted party lists at every institution it passes through. The mechanics of those checks account for a large share of unexplained delays.
What is being checked
Authorities publish lists of individuals, entities, vessels and sometimes entire sectors subject to restrictions. Institutions must not process payments involving them.
Lists differ between jurisdictions, and an institution generally applies every list relevant to the currencies and countries it operates in. A payment can be permissible in one jurisdiction and prohibited in another.
Restrictions also extend to entities owned or controlled by listed parties, which requires ownership analysis rather than a name comparison. Determining control is frequently ambiguous.
Why matching produces so many false positives
Names are transliterated differently between scripts, abbreviated inconsistently and shared by many unrelated people. Systems must therefore match approximately rather than exactly.
Loose matching catches variants but flags large numbers of innocent payments. Tight matching misses variants, which is the failure regulators penalise.
Institutions calibrate toward caution, so the great majority of alerts are false. Each still requires human review before the payment continues.
What happens when a payment is stopped
The payment is held pending review, and the sender is usually told only that it is under investigation. Institutions are often restricted in what they may disclose.
Additional information about the parties or the purpose may be requested, which requires the sender's bank to relay questions from an intermediary it may not identify. Rounds of questions take days.
Payments may be returned or, where a genuine match exists, frozen rather than returned. Frozen funds are reported to the relevant authority and released only by licence.
Why the currency matters as much as the parties
A payment in a given currency typically settles through banks in that currency's home country. The rules of that jurisdiction apply to the transaction.
Two parties in unrelated countries can therefore find their payment subject to a third country's restrictions purely through the currency chosen. Choosing a different settlement currency changes which rules apply.
This is a principal reason firms trading in restricted regions consider alternative settlement currencies. The exposure follows the settlement route.
How institutions manage the cost
Screening large volumes with high false positive rates is expensive, and the cost falls on payment processing generally. It is one reason some banks exit entire markets.
Better structured payment data improves matching accuracy and reduces alert volumes. Investment has concentrated there because the alternative is more staff.
Requirements, lists and permissible disclosures differ by jurisdiction and change frequently, so institutions treat this as an area of continuous adjustment rather than a fixed control.