The information in this article applies to administrations with the additional module Purchase to pay.
This message indicates that the purchase unit of the article does not match the unit in the purchase order, which prevents the booking from being processed. Most likely the unit of the article was changed in the meantime.
Solution: Check in the booking which purchase order line triggers the error message and match the article with the correct purchase unit. Adjust the purchase unit in Exact Online and export the invoice again. After the booking has been exported to Exact Online, the purchase unit can be adjusted again so that the latest configuration is restored.