This message appears when one or more contra account numbers (a.k.a "bank account" numbers) are not yet filled out in the Pleo Accounting page, and so the export fails.
Please double-check that a relevant contra/bank account account number for card expenses has been entered in Pleo:
If you're using Pocket, please make sure that you've filled out the contra/bank account numbers for Pocket expenses:
In English, a contra account (shown as "bank account" in Pleo) refers to a bank konto (Danish) in e-conomic. What's called a "chart of accounts" in English refers to your "kontoplan" (Danish) in e-conomic.
In English, a journal (also sometimes shown as "cashbook" in error messages), refers to a kassekladde (Danish) in e-conomic.