Invalid payment reference
/api/account/payments/[paymentRef]/invoice rejected the reference as empty/invalid (400).
Why this happens
Broken link, truncated URL, or bookmark without a valid paymentRef. Distinct from Invoice not found (valid format, no matching payment/invoice).
Diagnose and fix
1. Open the invoice from Payment history and invoices (do not edit the URL).
2. Sign in as the account that owns the payment.
3. If the payment never completed, there may be nothing to invoice yet.
4. Admin can locate the payment in Payment transactions list.