An export invoice carries a VAT registration for the buyer
Reported asbuyer_vat_registered_on_exporta buyer VAT registration on an export invoice
What is wrong
The invoice transaction code (KSA-2) has its exports flag at position 5 set to 1, and the buyer's party block carries a cac:PartyTaxScheme with a cbc:CompanyID in it. ZATCA rejects that under BR-KSA-46: the customer on an export invoice is outside the Kingdom and so has no Saudi VAT registration to state, and the field must be absent rather than empty or filled with a placeholder.
What to check in your ERP
Two things can be wrong here and they need opposite fixes. If the sale really is an export, the buyer's whole cac:PartyTaxScheme block must be left out of the document - not blanked, not zero-filled. Check whether your export template writes that block unconditionally for every customer, which is the usual cause. If the customer is inside the Kingdom and does have a VAT registration, then the exports flag is what is wrong: clear position 5 of the transaction code, so 0100000 rather than 0100100.