BR-02: Missing Invoice ID
BR-02 means the invoice has no non-empty identifier. Your accounting or invoicing system should provide the invoice number.
UBL location
/Invoice/cbc:ID
How to fix it
Add the invoice number inside <cbc:ID>. Do not invent a number if your accounting system has not assigned one.
RejectFix can detect this missing field. Passing this check does not guarantee Access Point acceptance.