This message comes up when at least one Pleo expense is from a merchant where there's an ampersand (&) in the name, but no space before and after the ampersand. For example, an expense with a merchant called "Fish&Chips Flughafen B" will fail to be exported to Pleo. To be exported in Datev, the name would need to be a space in "Fish & Chips". This is a requirement of Datev.
As it's not possible to change the name of the merchant on a Pleo expense, this requires a bit of extra work on your end. Thanks for your understanding. If you're not sure which one of the expenses in your export queue has this issue, please contact our support team and we'll help you.
The solution is to:
"Get rid" of this expense in Pleo by changing the connected export format from Datev Unternehmen Online to another system. In Pleo, go to the Accounting page, disconnect from DUO, and connect to a generic format such as Pleo's custom csv format.
Export only the affected expense(s). The export will just consist of downloading a file.
Create the expense manually in DUO.
Back in Pleo, reconnect to Datev Unternehmen Online.