When I try to book in Basecone, I get the following error message:
When you get this error message, this means that your Basecone user is disconnected or not linked to the accounting system. Without this connection, it will not be possible to book documents to the accounting system.
Click on the user icon on the top right of the page to go to your own user settings and then to the last tab "Accounting system users". See the image below as an example, click on Change credentials to enter the correct login credentials.
Or you can go to Settings > Users > Action (edit) > Accounting system Users (tab)