On the below link you can find a list of Units of Measures in  PEPPOL, so please check in BC thats your mapping between your setup BC match the PEPPOL codes

Here you can see how its done from  Danish GREEN to PEPPOL RED

Belkow Link to the offcial PEPPOL Units of Measure list

Peppol BIS Billing 3.0 | Rules

This will be the error if not setup is correct

{"message":"Invalid Document","errors":[{"context":"/Invoice[1]/InvoiceLine[1]/InvoicedQuantity[1]","pattern":"","text":"[BR-CL-23] [BR-CL-23]-Unit code MUST be coded according to the UN/ECE Recommendation 20 with\n      Rec 21 extension","isWarning":false},{"context":"/Invoice[1]/InvoiceLine[1]/Price[1]/BaseQuantity[1]","pattern":"","text":"[BR-CL-23] [BR-CL-23]-Unit code MUST be coded according to the UN/ECE Recommendation 20 with\n      Rec 21 extension","isWarning":false}]}'