The value of the Seller Party ID Scheme ID must be contained in ISO 6523 ICD [VRBL-CL-PINT-IdentificationSchemeID] or be contained in ISO 6523 ICD (Extended) [VRBL-CL-PINT-IdentificationSchemeID-Extended]. For more information visit: https://docs.peppol.eu/poacc/billing/3.0/codelist/ICD/
If the Seller Party ID is marked as a GLN, its 13th digit must be the correct checksum of the other 12 digits according to the GS1 check digit calculation.