This message indicates that the Free Textfield 3 is not set up in the accounting system for the document to be posted in Twinfield. You can set this up per journal.
Example: for purchase invoice you can find these settings in Twinfield when you go to
Settings > Company settings > Transaction types > purchase invoice.
Configure the following two settings:
Free text field 3
Usage --> Allowed
Link: copy & paste the link below to this field (see image below)
(Control this link when you paste this into the field that it's the same)
For more information, see article: Settings to retrieve invoices in Twinfield