DT-CIUS-PT-124.1
The BT-137 and BT-142 does not meet the defined format: decimal value with 2 decimal places and 13 unit places.
What the rule checks
As the rule set's publisher wrote it. The rule runs on every element the context matches, and fails where the test is false; the validator reports the line of that element.
//ubl:Invoice/cac:InvoiceLine/cac:AllowanceCharge/cbc:BaseAmount | //cn:CreditNote/cac:CreditNoteLine/cac:AllowanceCharge/cbc:BaseAmount
matches(.,'^(\d{1,13}\.\d{2})$')
Checked with Portugal CIUS-PT Invoice (UBL), Portugal CIUS-PT Credit Note (UBL)