Explanation:
The extended form in DATEV Unternehmen online supplements DATEV with the financial year. Each invoice contains an invoice date and if the corresponding year does not exist in DATEV Unternehmen online, the invoice cannot be assigned and this prevents the invoice from being made available.
Solution:
DATEV Unternehmen online is set to extended, in case of doubt only the tax office can do this for you. You can find out how this works here.
There are then 2 ways in which you can make your data available:
Delete the documents and remove them from the recycle bin. Then export the data from Candis again.
Open the document in DATEV Unternehmen online and add the existing financial year to the invoice.
Both solutions mean that your data can be provided and posted in DATEV Rechnungswesen.