UBL-SR-58
A Financial Institution Branch shall contain exactly one Payment service provider identifier (BT-86).
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.
cac:PaymentMeans
not(cac:PayeeFinancialAccount/cac:FinancialInstitutionBranch) or count(cac:PayeeFinancialAccount/cac:FinancialInstitutionBranch/cbc:ID) = 1
Checked with EN 16931 Invoice (UBL), EN 16931 Credit Note (UBL), Croatia eRačun Invoice (UBL), Croatia eRačun Credit Note (UBL)